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A combined DFT and SCRF study of solvent effects on 4-methyl-3-penten-2-one
Journal of Molecular Structure (Theochem) 459 (1999) 163–170
A combined DFT and SCRF study of solvent effects on 4-methyl-3-penten-2-one Shucheng Xu a, Chengdong Wang b, Guohe Sha a, Jinchun Xie a,*, Zhongzhi Yang c a
State Key Laboratory of Molecular Reaction Dynamics, DaLian Institute of Chemical Physics, Dalian 116023, People’s Republic of China b State Key Laboratory of Short Wavelength Chemical Lasers, DaLian Institute of Chemical Physics, Dalian 116023, People’s Republic of China c Department of Chemistry, Liaoning Normal University, Dalian 116023, People’s Republic of China Received 9 March 1999; accepted 5 June 1998
Abstract The IR spectrum of 4-methyl-3-penten-2-one is interpreted with the aid of normal coordinate calculations within the Onsager self-consistent reaction field (SCRF) model, using a density functional theory (DFT) method at the Becke3LYP/6-31G* level. The solvent effects on the geometry, energy, dipole moment, and vibrational frequencies of 4-methyl-3-penten-2-one in the solution and in the liquid phase are calculated using the Onsager SCRF model. The calculated vibrational frequencies in the liquid-phase are in good agreement with the experimental values. The solvent reaction field has generally weak influence. For the two main bands of CyC and CyO mixed vibrational modes, small frequency shifts (5–6 cm ⫺1), but relatively large changes in IR intensities (up to 101 km mol ⫺1 in the liquid phase) are found. 䉷 1999 Elsevier Science BV. All rights reserved. Keywords: DFT; SCRF; Solvent effects; 4-Methyl-3-penten-2-one
1. Introduction 4-Methyl-3-penten-2-one (mesityl oxide) is an important a ,b -unsaturated ketone molecule and a key intermediate in the synthesis of organometallic compounds. Its photochemistry, excited states and conformations have been experimentally studied [1–6]. Its standard infrared grating spectrum was obtained in 1970 [7]. Xu et al. [8] measured FT-IR and Raman spectra in the liquid phase, and calculated the vibrational spectra in the gas phase using ab initio methods at HF/3-21G and HF/6-31G* levels in previous work. In this work, we discuss solvent effects on its structure, energies, dipole moment and IR spectrum. * Corresponding author. E-mail: [email protected]
Solvent effects often play an important role in determining equilibrium constants and reaction rates. They can also affect p -facial selectivity, conformations, and other chemical and biochemical quantities. Currently, a continuum treatment of the bulk solvent through the quantwn mechanical implementation of the Onsager reaction field model [9] is widely employed using a modified molecular Hamiltonian to couple with the electric field of the solvent [10,11]. The ab initio SCRF formalism [12,13] commonly involves a bulk dielectric constant of the solvent and a spherical cavity surrounding the solute molecule. In mesityl oxide, there is a CyC–CyO skeleton, where time CyC double bond have an effect of p cloud conjugation with the CyO moiety; in addition, CyC and CyO stretching vibrations are both solventsensitive infrared stretching vibrations. Solvent
0166-1280/99/$ - see front matter 䉷 1999 Elsevier Science BV. All rights reserved. PII: S0166-128 0(98)00272-3
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Fig. 1. The stable conformer of s-cis for 4-methly-3-penten-2-one.
effects influence the IR spectrum, and other properties. We have assigned the vibrational modes of the most stable conformation of mesityl oxide, and compared the IR spectrum calculated by the Onsager SCRF theory at the B3LYP/6-31 G* [14,15] level with the experimental spectrum in the liquid phase [8]. We have also investigated time solvent effects on the molecule. 2. Computational details Ab initio calculations were performed with the GAUSSIAN 94 programs [16] on an IBM RS/6000 workstation. The geometry optimization and vibrational frequency calculations of the molecule in the gas phase, solutions, and liquid phase were carried by using the Onsager SCRF method and DFT at the B3LYP/6-31G* level. The molecular volume was calculated to estimate ao for the Onsager SCRF model at the B3LYP/6-31G* level, the SCRF geometry optimization began at the optimized gas phase structure, and the SCRF frequencies were calculated at the SCRF optimized structure. 3. Results and discussion 3.1. Geometry optimizations and structural comparison 4-Methyl-3-penten-2-one molecule has both strans and s-cis conformations, and the s-cis form is more stable (see Ref. [8]).
The optimized geometry of the stable conformer of the s-cis (see Fig. 1) in the gas phase is listed in Table 1. Comparing the values calculated at the B3LYP/6-3lG* level with the previous result at the HF/6-31G* level [8], we found that the CyC bond ˚ , the CyO bond length length increases 0.019 A ˚ , the C–H bond length increases increases 0.028 A ˚ , while changes in the CyC bond lengths about 0.01 A ˚ and bond angles change by less are less than 0.01 A than ^ 1⬚. From previous studies it is known that the DFT methods can achieve greater accuracy than the Hartree–Fock theory [15,17]. The calculated values at the B3LYP/6-31G* level are as follows: CyO bond
Table 1 Optimized geometry for a 4-methyl-3-penten-2-one a Coordinate b
Gas phase (1 1.0)
r(C2 –C1) r(C3 –C2) r(C4 –C3) r(C5 –C4) r(C6 –C4) r(O7 –C2) r(H8 –C1) r(H9 –C1) r(H10 –C1) r(H11 –C3) r(H12 –C5) r(H13 –C5) r(H14 –C5) r(H15–C6) r(H16 –C6) r(H17 –C6) ⬔(C1C2C3) ⬔(C2C3C4) ⬔(C3C4C5) ⬔(C3C4C6) ⬔(C3C207) ⬔(C2C1H8) ⬔(C2C1H9) ⬔(C2C1H10) ⬔(C2C3H11) ⬔(C4C5H12) ⬔(C4C5H13) ⬔(C4C5H14) ⬔(C4C6H15) ⬔(C4C6H16) ⬔(C4C6H17)
1.523 1.484 1.352 1.508 1.505 1.226 1.091 1.098 1.098 1.089 1.094 1.099 1.099 1.088 1.099 1.099 114.93 128.04 119.88 125.08 124.85 109.60 110.60 110.60 114.53 112.45 110.55 110.55 112.06 109.81 109.81
a
Calculations at the B3LYP/6-31G* level. ˚ ), See Fig. 1 for atom numbering; bond lengths in angstro¨ms (A bond angles in degrees (⬚). b
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Table 2 The changes of the skeletal bond angles from the gas phase to solutions or liquid phase for 4-methyl-3-penten-2-one a Coordinate b ⬔(C1C2C3) ⬔(C2C3C4) ⬔(C3C4C5) ⬔(C3C4C6) ⬔(C3C2O7)
Solution (1 5.708) c
(1 10.65) d
Liquid phase (1 15.4)
⫺ 0.19 0.09 0.07 ⫺ 0.10 0.27
⫺ 0.19 0.09 0.07 ⫺ 0.10 0.27
⫺ 0.21 0.13 0.08 ⫺ 0.13 0.33
a
Calculations at the B3LYP/6-31G* level. See Fig. 1 for atom numbering; bond angles in degrees. c Solvent (1 5.708) is chlorobenzene. d Solvent (1 10.65) is 1,2-dichloroethane. b
˚ , CyC bond length 1.352 A ˚ , and C–C length 1.226 A ˚ bond lengths 1.484–1.523 A. The experimental values are as follows [14]: the CyO bond length is ˚ , the CyC is 1.507 A ˚ for acetone, and the 1.222 A ˚ CyC bond length is 1.345 A for trans-1,3-butadiene. Obviously, our calculated values are in good agreement with these experimental data. The effects of the medium on the molocular geometry of 4-methyl-3-penten-2-one were investigated by the Onsager reaction field theory. The radius a0 of the molecular volume calculated at the B3LYP/6-31G* ˚ . Its geometry was optimized with the level is 4.30 A solvents of chlorobenzene (1 5.078) [18], 1,2dichloroethane (1 10.65) [18] solution, and the pure liquid phase (1 15.4) [19], respectively. Compared with the gas phase, bond lengths are generally the same, only C–C, CyC, and CyO bond lengths
˚ ). Compared with bond increase slightly (0.0001 A lengths, skeletal bond angles exhibit a significant change (Table 2), ⬔C1C2C3 and ⬔C3C4C6 decrease 0.19⬚ and 0.10⬚ in the solution, and decrease 0.21⬚ and 0.13⬚ in the liquid phase, respectively; on time other hand, ⬔C3C2O7, ⬔C2C3C4 and ⬔C3C4C5, increase 0.27⬚, 0.09⬚ and 0.07⬚ in the solution, and 0.33⬚, 0.13⬚ and 0.08⬚ in the liquid phase, respectively. In general, the solvent reaction field has only weak influence on the bond lengths and skeletal bond angles. 3.2. Solvent effects on other properties Solvent effects are important in molecular thermodynamic properties, including zero-point vibrational energy (ZPVE), enthalpy, free energy, polarization
Table 3 Energies for 4-methyl-3-penten-2-one a
ZPVE e Enthalpy GFE f PE g total energy
Gas phase (1 1.0)
Solution b (1 5.708) c
(1 10.65) d
Liquid phase b (1 15.4)
91.870 98.003 70.724 0.000 ⫺ 309.729693
0.010 ⫺ 0.004 0.066 ⫺ 0.703 ⫺ 0.615
0.010 ⫺ 0.005 0.066 ⫺ 0.829 ⫺ 0.716
0.011 ⫺ 0.005 0.072 ⫺ 0.882 ⫺ 0.754
Calculations at the B3LYP/6-31G* level. The unit of total energy in the gas phase is hartree, and the unit of other energy is kcal mol ⫺1. Changes of the energy from the gas phase to solutions or liquid phase. c Solvent (1 5.708) is chlorobenzene. d Solvent (1 10.65) is 1,2-dichloroethane. e Zero point vibrational energy. f Gibbs free energy. g Polarization energy. a
b
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Fig. 2. (a) The experimental IR spectrum in the liquid phase. (b) Ab initio SCRF calculated IR spectrum in the liquid phase at time B31YP/631G* level.
energy and total energy. The calculated energies at the B3LYP/6-31G* level for 4-methyl-3-penten-2-one in the gas phase, solutions and liquid phase are given in Table 3. ZPVE is needed for theoretical studies of thermochemistry. The ZPVE in the gas phase is 91.870 kcal mol ⫺1. Comparing the gas phase, time ZPVE increases 0.01 kcal mol ⫺1 in the two solutions, and 0.11 kcal mol ⫺1 in the liquid phase. The enthalpy in the gas phase is 98.003 kcal mol ⫺1. Comparatively, the enthalpies in chlorobenzene, 1,2dichloroethane solution, and in liquid phase, decreases 0.004, 0.005 and 0.005 kcal mol ⫺1, respectively. Gibbs free energy of the gas phase is 70.724 kcal mol ⫺1. For the two solutions and liquid phase, free energies increase 0.066, 0.066 and 0.072 kcal mol ⫺1. The polarization energies in the medium, along with increasing dielectric constants of the solvent,
become much lower, from ⫺0.702, to ⫺0.829, 0.882 kcal mol ⫺1. The total energy in the gas phase is ⫺ 309.72869 hartrees. In comparison with the gas phase, the total energies in the solutions and liquid phase become much lower, decrease 0.615, 0.7l6 and 0.754 kcal mol ⫺1, respectively. Hence, the molecule in medium is more stable than the neutral. In addition, the corresponding dipole moments increase in going from the gas phase to solutions to liquid phase, 0.350 (1 5.708), 0.404 (1 10.65) and 0.432 (1 15.4) Debye, respectively. Therefore, the molecular polarity in medium is little stronger than that in the neutral. 3.3. Assignment of vibrational frequencies The ab initio calculated frequencies in the liquid phase were obtained using the Onsager reaction field model at the B3LYP/6-31G* level. Normal mode
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Table 4 Calculated and experimental vibrational frequencies and potential energy distributions for 4-methyl-3-penten-2-one in the liquid phase a
no.
B3LYP/6-31G* Scaled b
Int. (IR) c
n1 n2 n3 n4 n5 n6 n7 n8 n9 n10 n11 n12
3013* 2978* 2973* 2954* 2920* 2904* 2893* 2867* 2860* 2853* 1703 1618
3.4 28.0 18.1 17.5 13.3 27.0 12.1 3.3 50.1 15.0 142.2 314.6
n13 n14 n15 n16 n17 n18 n19 n20 n21 n22 n23 n24 n25 n26 n27 n28 n29 n30 n31 n32 n33 n34 n35 n36
1476 1457 1446 1445 1440 1436 1388 1382 1357 1350 1209 1155 1078 1067 1011 979 943 933 886 830 799 604 582 450
16.3 56.0 0.6 11.8 6.4 46.6 4.0 30.0 42.0 11.0 61.3 105.6 2.3 19.5 7.6 5.5 75.2 3.9 5.4 9.1 1.8 35.2 0.8 3.2
n37 n38 n39 n40 n41 n42 n43 n44 n45
424 363 327 206 200 144 115 97 54
0.8 4.4 2.2 6.0 0.7 0.2 0.0 0.6 3.5
Experimental d Freq.
Int. (IR)
3003 2978 2939 2914
w sh w w w
2855
w sh
1689 1619
s s
1449
m
1425
m sh
1380 1357
m m
1220 1166
m m
1069 1019
w w
965
m
900 822
w w
622
m
459
w
P.E.D. (%) e
Sym. spec. f
Me3 as1(99) H11C3 S(91), Me2 as1(8) Me1 as1(99) Me2 as1(90), H11C3 S(8) Me1 as2(99) Me2 as2(90), Me3 as2(7) Me3 as2(90), Me2 as2(8) Me1 ss(99) Me2 ss(60), Me3 ss(40) Me3 ss(60), Me2 ss(40) O7yC2 s(62), C4yC3 s(15), Me1 ab1(15) C4yC3 s(47), Me3 ab1(19), Me2 ab1(14), O7yC2 s(11) Me3 ab2(67), Me2 ab2(33) Me2 ab1(46), Me3 ab1(13) Me1 ab2(61), Me2 ab2(18), Me3 ab2(7) Me2 ab2(47), Me1 ab2(25), Me3 ab2(17) Me3 ab1(46), Me2 ab1(20), Me1 ab1(10) Me1 ab1(60), Me3 ab1(14) Me3 sb(26), Me2 sb(20) Me2 sb(30), H11C3 in-plane b(22), Me3 sb(9) Me1 sb(44), H11C3 in-plane b(14), Me3 sb(10) H11C3 in-plane b(40), Me3 sb(18), Me2 sb(17) Me3 r1(30), Me1 r1(24), Me2 r1(14) Me1 r1(28), H11C3 in-plane b(22), Me2 r1(11) Me3 r1(36), Me2 r2(35) Me2 r1(35), Me3 r1(23), Me1 r1(15) Me1 r2(80), Me2 r2(10) Me2 r2(35), Me3 r1(33), H11C3 out-of-plane(22) C2C1 s(40), C3C2 s(32), C5C4 s(21) C2C3C4 b(38), C3C4C6 b(15) C3C2 s(40), C2C1 s(27), C5C4 s(18), C6C4 s(14) H11C3 out-of-plane(68), Me2 r2(11), Me3 r2(6) C5C4 s(27), C6C4 s(20), C2C1 S(15) O7yC2 in-plane b(65), C2C3C4 b(24) O7yC2 out-of-plane(60), H11C3 out-of-plane(8) C4yC3 out-of-plane(70), O7yC2 out-ofplane(17) C6C4 s(40), C3C2 s(20), C5C4 s(14) C3C4C6 b(38), C1C2C3 b(23), C3C4C5 b(15) C3C4C5 b(26), C1C2C3 b(22), C3C4C6 b(20) C1C2C3 b(26), C3C4C6 b(14), C2C3C4 b(10) Me2 t(34), Me1 t(14), O7yC2 out-of-plane(10) C3C2 t(30), Me2 t(18), Me3 t(16) Me1 t(68), Me3 t(9) Me3 t(52), Me2 t(17), Me1 t(5) C4yC3 t(60), C3C2 t(30)
A0 A0 A0 A0 A 00 A 00 A 00 A0 A0 A0 A0 A0 A 00 A0 A 00 A 00 A0 A0 A0 A0 A0 A0 A0 A0 A 00 A0 A 00 A 00 A0 A0 A0 A 00 A0 A0 A 00 A 00 A0 A0 A0 A 00 A0 A 00 A 00 A 00 A 00
˚. Onsager SCRF Model, a0 4.30 A Frequencies in cm -1. Scaling factor using 0.96, except for * using 0.94. c IR intensity in km mol ⫺1. d See Ref. [8], w weak, m middle, sh shoulder, s strong, v very. e P.E.D. (potential energy distributions): s, stretch; ss, symmetric stretch; as, antisymmetric stretch; b, bend; sb, symmetric bend; ab, antisymmetric bend; r, rock; t, torsion; Me, methyl. f Symmetry species. a
b
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calculations were completed using the Wilson GF method [20]. The potential energy distributions of the vibrational modes are calculated by the normal mode analysis. The calculated and experimental frequencies their intensities, potential energy distributions and symmetry species are given in Table 4. The experimental and calculated IR spectra in the liquid phase are compared in Fig. 2. The ab initio calculated frequencies are usually larger than the corresponding experimental values and contain known systematic errors due to the neglect of anharmonicity and electron correlation [14,21]. Therefore, it is usual to scale frequencies predicted at the B3LYP/6-31G* level including some of the effects of electron correlation by an empirical factor of 0.96 [15,22]. However, for a particular molecule, there are some difference for systematic errors of calculated frequencies of different vibrational modes [23,24]. For 4-methyl-3-penten-2one, we scaled the calculated frequencies at the B3LYP/6-31G* level using the scaling factor of 0.96, except for CH3 and C–H stretching modes using that of 0.94 due to strong effect of anharmonicity [21]. The stable conformer of 4-methyl-3-penten-2-one (see Fig. 1) belongs to Cs point group and 45 normal mode vibrational frequencies span the irreducible representations 28 A 0 ⫹ 17 A 00 . Comparing with the observed ones, the average error of the scaled calculated frequencies of IR spectrum was 10 cm ⫺1. Therefore, the scaled calculated frequencies using the DFT method at the B3LYP/6-3lG* level are in good agreement with the experimental values. In detail, the observed weak IR shoulder peak at 3003 cm ⫺1 is assigned to H11C3 s(91) Me2 as1(8) mode calculated at 2978 cm ⫺1. For the weak IR peaks at 2978, 2939 and 2914 cm ⫺1 are assigned to Me1 as1(99) calculated at 2973 cm ⫺1, Me2 as1(90) H11C3 s(8) mode calculated at 2954 cm ⫺1, and Me2 as2(90) mode calculated at 2920 cm ⫺1, respectively. The observed weak IR shoulder peak at 2855 cm ⫺1 is assigned to Me2 ss(60) Me3 ss(40) mode calculated at 2860 cm ⫺1. The strongest IR peak observed near 1689 cm ⫺1 is assigned to O7yC2 s(62) C4yC3 s(15) Me1 ab1(l5) mode of 1703 cm ⫺1. The next strongest IR peak observed at 1619 cm ⫺1 is assigned to C4yC3 s(47) Me3 ab1(19) Me2 ab1(14) O7yC2 s(11) mode of 1618 cm ⫺1. The observed middle IR peak at
1449 cm ⫺1 and middle IR shoulder peak at 1425 cm ⫺1 are assigned to Me2 ab1(46) Me3 ab1(13) mode calculated at 1457 cm ⫺1 and Me1 ab1(60) Me3 ab1(14) mode calculated at 1436 cm ⫺1, respectively. The observed middle IR peaks at 1380 and 1357 cm ⫺1 are assigned to Me2 sb(30) H11C3 in-plane b(22) Me3 sb(9) mode calculated at 1382 cm ⫺1 and Me1 sb(44) H11C3 in-plane b(14) Me3 sb(10) mode calculated at 1357 cm ⫺1, respectively. The observed middle IR peaks at 1220, 1166 cm ⫺1 and weak IR peak at 1069 cm ⫺1 are assigned to Me3 r1(30) Me1 r1(24) Me2 r1(14) mode of 1209 cm ⫺1, Me1 r1(28) H11C3 inplane b(22) Me2 r1(11) mode of 1155 cm ⫺1, and Me2 r1(35) Me3 r1(23) Me1 r1(15) mode of 1067 cm ⫺1, respectively. The observed weak IR peaks at 1019 and 822 cm ⫺1 are assigned to Me1 r2(80) Me2 r2(10) mode of 1011 cm ⫺1 and H11C3 out of plane(68) Me2 r2(11) Me3 r2(6) mode of 830 cm ⫺1, respectively. The observed middle and weak IR peaks at 965 and 900 cm ⫺1 are assigned to C2C1 s(40) C3C2 s(32) C5C4 s(21) mode of 943 cm ⫺1 and C3C2 s(40) C2C1 s(27) C5C4 s(18) C6C4 s(14) mode of 830 cm ⫺1, respectively. The observed middle and weak IR peaks at 622 and 459 cm ⫺1 are assigned to O7yC2 in-plane b (65) C2C3C4 b (24) mode of 604 cm ⫺1 and C4yC3 out-of-plane(70) O7yC2 out-of-plane(17) mode of 450 cm ⫺1, respectively. In Table 4, each frequency corresponds to a different vibrational mode which is principal in potential energy distributions. Fig. 2 displays the, experimental and calculated IR spectra in the liquid phase. It has shown that calculated peaks are in good agreement with experimental peaks. Note that some calculated peaks getting close to each other cannot be distinguished in the experimental spectra, and some calculated lines of lower intensities are not observed in the experimental spectra. 3.4. The solvent effects on the infrared spectra The shifts of frequencies and changes of IR intensities from the gas phase to medium are listed in Table 5. On going from the gas phase to solutions and liquid phase, shifts of frequencies are nearly same in chlorobenzene and 1,2-dichchloroethane solutions. In the liquid phase, there is small frequency shifts for
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Table 5 Calculated vibrational frequencies for 4-methyl-3-penten-2-one in the gas phase, solutions, and liquid phase a
no.
Gas phase (1 1.0) Freq. (Cal.) e
n1 n2 n3 n4 n5 n6 n7 n8 n9 n10 n11 n12 n13 n14 n15 n16 n17 n18 n19 n20 n21 n22 n23 n24 n25 n26 n27 n28 n29 n30 n31 n32 n33 n34 n35 n36 n37 n38 n39 n40 n41 n42 n43 n44 n45
3204 3168 3155 3132 3101 3082 3072 3045 3037 3029 1777 1690 1536 1518 1505 1503 1497 1494 1443 1438 1413 1404 1257 1201 1122 1110 1053 1019 981 971 921 861 831 629 604 467 441 378 340 215 209 150 112 96 55
Int. (IR) f
Solution b (1 5.708) c Freq. (Cal)
Int. (IR)
(1 10.65) Freq. (Cal)
2.7 14.3 20.7 16.3 13.3 28.3 8.1 3.3 44.4 7.4 110.5 213.4 14.8 35.1 0.4 10.0 5.4 31.4 1.6 22.3 34.2 4.8 45.9 70.0 1.8 13.2 6.3 4.7 51.1 1.6 2.9 7.3 1.0 25.0 0.7 2.8 0.6 2.7 1.6 3.9 0.5 0.1 0.0 0.8 2.8
⫺3 ⫺4 3 4 1 2 1 1 1 1 ⫺4 ⫺5 0 ⫺1 0 0 0 0 1 0 ⫺1 0 1 0 0 0 1 1 1 0 0 1 0 ⫺1 1 1 1 0 0 ⫺1 ⫺1 0 6 5 1
0.6 10.5 ⫺ 1.8 1.1 0.1 ⫺ 0.8 3.2 0.0 5.3 5.7 25.8 80.1 1.2 16.3 0.1 1.5 0.7 12.0 1.8 6.2 6.9 4.4 12.4 28.4 0.4 5.0 1.1 0.7 19.3 1.8 1.8 1.5 0.6 8.1 0.1 0.3 0.1 1.3 0.5 1.7 0.2 0.1 0.1 ⫺ 0.1 0.6
⫺3 ⫺4 3 4 1 2 1 1 1 1 ⫺4 ⫺5 0 ⫺1 0 0 0 0 1 0 ⫺1 0 1 0 0 0 ⫺1 ⫺1 ⫺1 0 0 1 0 0 1 1 1 0 0 ⫺1 ⫺1 0 6 5 1
d
Int. (IR) 0.7 12.4 ⫺ 2.0 1.3 0.0 ⫺ 0.9 3.6 0.0 6.2 6.6 30.4 94.2 1.4 19.3 0.1 1.8 0.8 14.1 2.2 7.3 8.2 5.3 14.6 33.9 0.5 5.9 1.3 0.7 23.1 2.0 2.1 1.7 0.7 9.7 0.1 0.4 0.2 1.6 0.5 2.0 0.2 0.1 0.1 ⫺ 0.1 0.7
˚. Onsager SCRF Model at the B3IYP/6-31G(d) level, a0 4.30A Shifts of frequencies and changes of IR intensities from the gas phase to solutions, or liquid phase. c Solvent (1 5.708) is chlorobenzene. d Solvent (1 10.65) is 1,2-dichloroethane. e Frequence in cm ⫺1. f IR intensity in km mol ⫺1. a
b
Liquid phase b (1 15.4) Freq. (Cal) ⫺3 ⫺4 4 5 1 2 1 1 2 1 ⫺5 ⫺6 0 ⫺2 0 ⫺1 1 0 1 0 ⫺1 0 1 0 0 0 ⫺1 ⫺1 ⫺1 0 1 2 0 ⫺ 1 1 1 1 0 0 ⫺1 ⫺1 0 7 5 1
lnt. (IR) 0.7 13.7 ⫺ 2.5 1.2 0.0 ⫺ 1.2 4.0 0.0 5.7 7.6 31.7 101.2 1.5 20.9 0.2 1.8 1.0 15.2 2.4 7.7 7.8 6.2 15.4 35.6 0.5 6.3 1.3 0.8 24.1 2.3 2.5 1.8 0.8 10.2 0.1 0.4 0.2 1.7 0.6 2.1 0.2 0.1 0.0 ⫺ 0.1 0.7
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n1, n2, n3, n4, n11, n12, n43 and n44. Where, n1 and n2 are Me3 antisymmetric stretching and C–H stretching vibrations, red shifts about 3–4 cm ⫺1; n11 and n12 are mixed modes of O7yC2 and C4yC3 stretching vibrations, red shifts about 5–6 cm ⫺1. However, n3 and n4 are Me1 and Me2 antisymmetric stretching vibrations, blue shifts about 4–5 cm ⫺1; n43 and n44 are methyl torsion modes, blue shifts about 5–7 cm ⫺1. In general, on going from the gas phase to liquid phase, most absorption peaks become sronger, where the strong IR peaks in the gas phase become much stronger in medium. For instance, significant changes of IR intensities are observed in n11, n12, n14, n24, n29, where, n12 of C4yC3 and O7yC2 mixed mode has the largest changes in intensities (up to 101 km mol ⫺1 in the liquid phase). 4. Conclusions We have found mesityl oxide has a stable conformation of s-cis, the optinmized geometry is in good agreement with the experimental data. On going from the gas phase to solutions and liquid phase, the solvent reaction field has general weak influence on the skeletal bond angles, dipole moment, and thermodynamics properties of the molecule. The scaled calculated frequencies using the Onsager SCRF model at the B31YP/6-31G* level are all in good agreement with the experimental values. The infrared spectrum of the molecule is weak influenced by the solvent reaction field. Specially, for the two main bands of CyC and CyO mixed vibrational modes, small frequency shifts (5–6 cm ⫺1), but relatively large changes of intensities (up to 101 km mol ⫺1 in the liquid phase) are found.
Acknowledgements This work was supported in part by grants from the National Science Foundation of China and State Key Laboratory of Short Wavelength Chemical Lasers.
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A combined DFT and SCRF study of solvent effects on 4-methyl-3-penten-2-one Shucheng Xu a, Chengdong Wang b, Guohe Sha a, Jinchun Xie a,*, Zhongzhi Yang c a
State Key Laboratory of Molecular Reaction Dynamics, DaLian Institute of Chemical Physics, Dalian 116023, People’s Republic of China b State Key Laboratory of Short Wavelength Chemical Lasers, DaLian Institute of Chemical Physics, Dalian 116023, People’s Republic of China c Department of Chemistry, Liaoning Normal University, Dalian 116023, People’s Republic of China Received 9 March 1999; accepted 5 June 1998
Abstract The IR spectrum of 4-methyl-3-penten-2-one is interpreted with the aid of normal coordinate calculations within the Onsager self-consistent reaction field (SCRF) model, using a density functional theory (DFT) method at the Becke3LYP/6-31G* level. The solvent effects on the geometry, energy, dipole moment, and vibrational frequencies of 4-methyl-3-penten-2-one in the solution and in the liquid phase are calculated using the Onsager SCRF model. The calculated vibrational frequencies in the liquid-phase are in good agreement with the experimental values. The solvent reaction field has generally weak influence. For the two main bands of CyC and CyO mixed vibrational modes, small frequency shifts (5–6 cm ⫺1), but relatively large changes in IR intensities (up to 101 km mol ⫺1 in the liquid phase) are found. 䉷 1999 Elsevier Science BV. All rights reserved. Keywords: DFT; SCRF; Solvent effects; 4-Methyl-3-penten-2-one
1. Introduction 4-Methyl-3-penten-2-one (mesityl oxide) is an important a ,b -unsaturated ketone molecule and a key intermediate in the synthesis of organometallic compounds. Its photochemistry, excited states and conformations have been experimentally studied [1–6]. Its standard infrared grating spectrum was obtained in 1970 [7]. Xu et al. [8] measured FT-IR and Raman spectra in the liquid phase, and calculated the vibrational spectra in the gas phase using ab initio methods at HF/3-21G and HF/6-31G* levels in previous work. In this work, we discuss solvent effects on its structure, energies, dipole moment and IR spectrum. * Corresponding author. E-mail: [email protected]
Solvent effects often play an important role in determining equilibrium constants and reaction rates. They can also affect p -facial selectivity, conformations, and other chemical and biochemical quantities. Currently, a continuum treatment of the bulk solvent through the quantwn mechanical implementation of the Onsager reaction field model [9] is widely employed using a modified molecular Hamiltonian to couple with the electric field of the solvent [10,11]. The ab initio SCRF formalism [12,13] commonly involves a bulk dielectric constant of the solvent and a spherical cavity surrounding the solute molecule. In mesityl oxide, there is a CyC–CyO skeleton, where time CyC double bond have an effect of p cloud conjugation with the CyO moiety; in addition, CyC and CyO stretching vibrations are both solventsensitive infrared stretching vibrations. Solvent
0166-1280/99/$ - see front matter 䉷 1999 Elsevier Science BV. All rights reserved. PII: S0166-128 0(98)00272-3
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Fig. 1. The stable conformer of s-cis for 4-methly-3-penten-2-one.
effects influence the IR spectrum, and other properties. We have assigned the vibrational modes of the most stable conformation of mesityl oxide, and compared the IR spectrum calculated by the Onsager SCRF theory at the B3LYP/6-31 G* [14,15] level with the experimental spectrum in the liquid phase [8]. We have also investigated time solvent effects on the molecule. 2. Computational details Ab initio calculations were performed with the GAUSSIAN 94 programs [16] on an IBM RS/6000 workstation. The geometry optimization and vibrational frequency calculations of the molecule in the gas phase, solutions, and liquid phase were carried by using the Onsager SCRF method and DFT at the B3LYP/6-31G* level. The molecular volume was calculated to estimate ao for the Onsager SCRF model at the B3LYP/6-31G* level, the SCRF geometry optimization began at the optimized gas phase structure, and the SCRF frequencies were calculated at the SCRF optimized structure. 3. Results and discussion 3.1. Geometry optimizations and structural comparison 4-Methyl-3-penten-2-one molecule has both strans and s-cis conformations, and the s-cis form is more stable (see Ref. [8]).
The optimized geometry of the stable conformer of the s-cis (see Fig. 1) in the gas phase is listed in Table 1. Comparing the values calculated at the B3LYP/6-3lG* level with the previous result at the HF/6-31G* level [8], we found that the CyC bond ˚ , the CyO bond length length increases 0.019 A ˚ , the C–H bond length increases increases 0.028 A ˚ , while changes in the CyC bond lengths about 0.01 A ˚ and bond angles change by less are less than 0.01 A than ^ 1⬚. From previous studies it is known that the DFT methods can achieve greater accuracy than the Hartree–Fock theory [15,17]. The calculated values at the B3LYP/6-31G* level are as follows: CyO bond
Table 1 Optimized geometry for a 4-methyl-3-penten-2-one a Coordinate b
Gas phase (1 1.0)
r(C2 –C1) r(C3 –C2) r(C4 –C3) r(C5 –C4) r(C6 –C4) r(O7 –C2) r(H8 –C1) r(H9 –C1) r(H10 –C1) r(H11 –C3) r(H12 –C5) r(H13 –C5) r(H14 –C5) r(H15–C6) r(H16 –C6) r(H17 –C6) ⬔(C1C2C3) ⬔(C2C3C4) ⬔(C3C4C5) ⬔(C3C4C6) ⬔(C3C207) ⬔(C2C1H8) ⬔(C2C1H9) ⬔(C2C1H10) ⬔(C2C3H11) ⬔(C4C5H12) ⬔(C4C5H13) ⬔(C4C5H14) ⬔(C4C6H15) ⬔(C4C6H16) ⬔(C4C6H17)
1.523 1.484 1.352 1.508 1.505 1.226 1.091 1.098 1.098 1.089 1.094 1.099 1.099 1.088 1.099 1.099 114.93 128.04 119.88 125.08 124.85 109.60 110.60 110.60 114.53 112.45 110.55 110.55 112.06 109.81 109.81
a
Calculations at the B3LYP/6-31G* level. ˚ ), See Fig. 1 for atom numbering; bond lengths in angstro¨ms (A bond angles in degrees (⬚). b
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Table 2 The changes of the skeletal bond angles from the gas phase to solutions or liquid phase for 4-methyl-3-penten-2-one a Coordinate b ⬔(C1C2C3) ⬔(C2C3C4) ⬔(C3C4C5) ⬔(C3C4C6) ⬔(C3C2O7)
Solution (1 5.708) c
(1 10.65) d
Liquid phase (1 15.4)
⫺ 0.19 0.09 0.07 ⫺ 0.10 0.27
⫺ 0.19 0.09 0.07 ⫺ 0.10 0.27
⫺ 0.21 0.13 0.08 ⫺ 0.13 0.33
a
Calculations at the B3LYP/6-31G* level. See Fig. 1 for atom numbering; bond angles in degrees. c Solvent (1 5.708) is chlorobenzene. d Solvent (1 10.65) is 1,2-dichloroethane. b
˚ , CyC bond length 1.352 A ˚ , and C–C length 1.226 A ˚ bond lengths 1.484–1.523 A. The experimental values are as follows [14]: the CyO bond length is ˚ , the CyC is 1.507 A ˚ for acetone, and the 1.222 A ˚ CyC bond length is 1.345 A for trans-1,3-butadiene. Obviously, our calculated values are in good agreement with these experimental data. The effects of the medium on the molocular geometry of 4-methyl-3-penten-2-one were investigated by the Onsager reaction field theory. The radius a0 of the molecular volume calculated at the B3LYP/6-31G* ˚ . Its geometry was optimized with the level is 4.30 A solvents of chlorobenzene (1 5.078) [18], 1,2dichloroethane (1 10.65) [18] solution, and the pure liquid phase (1 15.4) [19], respectively. Compared with the gas phase, bond lengths are generally the same, only C–C, CyC, and CyO bond lengths
˚ ). Compared with bond increase slightly (0.0001 A lengths, skeletal bond angles exhibit a significant change (Table 2), ⬔C1C2C3 and ⬔C3C4C6 decrease 0.19⬚ and 0.10⬚ in the solution, and decrease 0.21⬚ and 0.13⬚ in the liquid phase, respectively; on time other hand, ⬔C3C2O7, ⬔C2C3C4 and ⬔C3C4C5, increase 0.27⬚, 0.09⬚ and 0.07⬚ in the solution, and 0.33⬚, 0.13⬚ and 0.08⬚ in the liquid phase, respectively. In general, the solvent reaction field has only weak influence on the bond lengths and skeletal bond angles. 3.2. Solvent effects on other properties Solvent effects are important in molecular thermodynamic properties, including zero-point vibrational energy (ZPVE), enthalpy, free energy, polarization
Table 3 Energies for 4-methyl-3-penten-2-one a
ZPVE e Enthalpy GFE f PE g total energy
Gas phase (1 1.0)
Solution b (1 5.708) c
(1 10.65) d
Liquid phase b (1 15.4)
91.870 98.003 70.724 0.000 ⫺ 309.729693
0.010 ⫺ 0.004 0.066 ⫺ 0.703 ⫺ 0.615
0.010 ⫺ 0.005 0.066 ⫺ 0.829 ⫺ 0.716
0.011 ⫺ 0.005 0.072 ⫺ 0.882 ⫺ 0.754
Calculations at the B3LYP/6-31G* level. The unit of total energy in the gas phase is hartree, and the unit of other energy is kcal mol ⫺1. Changes of the energy from the gas phase to solutions or liquid phase. c Solvent (1 5.708) is chlorobenzene. d Solvent (1 10.65) is 1,2-dichloroethane. e Zero point vibrational energy. f Gibbs free energy. g Polarization energy. a
b
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Fig. 2. (a) The experimental IR spectrum in the liquid phase. (b) Ab initio SCRF calculated IR spectrum in the liquid phase at time B31YP/631G* level.
energy and total energy. The calculated energies at the B3LYP/6-31G* level for 4-methyl-3-penten-2-one in the gas phase, solutions and liquid phase are given in Table 3. ZPVE is needed for theoretical studies of thermochemistry. The ZPVE in the gas phase is 91.870 kcal mol ⫺1. Comparing the gas phase, time ZPVE increases 0.01 kcal mol ⫺1 in the two solutions, and 0.11 kcal mol ⫺1 in the liquid phase. The enthalpy in the gas phase is 98.003 kcal mol ⫺1. Comparatively, the enthalpies in chlorobenzene, 1,2dichloroethane solution, and in liquid phase, decreases 0.004, 0.005 and 0.005 kcal mol ⫺1, respectively. Gibbs free energy of the gas phase is 70.724 kcal mol ⫺1. For the two solutions and liquid phase, free energies increase 0.066, 0.066 and 0.072 kcal mol ⫺1. The polarization energies in the medium, along with increasing dielectric constants of the solvent,
become much lower, from ⫺0.702, to ⫺0.829, 0.882 kcal mol ⫺1. The total energy in the gas phase is ⫺ 309.72869 hartrees. In comparison with the gas phase, the total energies in the solutions and liquid phase become much lower, decrease 0.615, 0.7l6 and 0.754 kcal mol ⫺1, respectively. Hence, the molecule in medium is more stable than the neutral. In addition, the corresponding dipole moments increase in going from the gas phase to solutions to liquid phase, 0.350 (1 5.708), 0.404 (1 10.65) and 0.432 (1 15.4) Debye, respectively. Therefore, the molecular polarity in medium is little stronger than that in the neutral. 3.3. Assignment of vibrational frequencies The ab initio calculated frequencies in the liquid phase were obtained using the Onsager reaction field model at the B3LYP/6-31G* level. Normal mode
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167
Table 4 Calculated and experimental vibrational frequencies and potential energy distributions for 4-methyl-3-penten-2-one in the liquid phase a
no.
B3LYP/6-31G* Scaled b
Int. (IR) c
n1 n2 n3 n4 n5 n6 n7 n8 n9 n10 n11 n12
3013* 2978* 2973* 2954* 2920* 2904* 2893* 2867* 2860* 2853* 1703 1618
3.4 28.0 18.1 17.5 13.3 27.0 12.1 3.3 50.1 15.0 142.2 314.6
n13 n14 n15 n16 n17 n18 n19 n20 n21 n22 n23 n24 n25 n26 n27 n28 n29 n30 n31 n32 n33 n34 n35 n36
1476 1457 1446 1445 1440 1436 1388 1382 1357 1350 1209 1155 1078 1067 1011 979 943 933 886 830 799 604 582 450
16.3 56.0 0.6 11.8 6.4 46.6 4.0 30.0 42.0 11.0 61.3 105.6 2.3 19.5 7.6 5.5 75.2 3.9 5.4 9.1 1.8 35.2 0.8 3.2
n37 n38 n39 n40 n41 n42 n43 n44 n45
424 363 327 206 200 144 115 97 54
0.8 4.4 2.2 6.0 0.7 0.2 0.0 0.6 3.5
Experimental d Freq.
Int. (IR)
3003 2978 2939 2914
w sh w w w
2855
w sh
1689 1619
s s
1449
m
1425
m sh
1380 1357
m m
1220 1166
m m
1069 1019
w w
965
m
900 822
w w
622
m
459
w
P.E.D. (%) e
Sym. spec. f
Me3 as1(99) H11C3 S(91), Me2 as1(8) Me1 as1(99) Me2 as1(90), H11C3 S(8) Me1 as2(99) Me2 as2(90), Me3 as2(7) Me3 as2(90), Me2 as2(8) Me1 ss(99) Me2 ss(60), Me3 ss(40) Me3 ss(60), Me2 ss(40) O7yC2 s(62), C4yC3 s(15), Me1 ab1(15) C4yC3 s(47), Me3 ab1(19), Me2 ab1(14), O7yC2 s(11) Me3 ab2(67), Me2 ab2(33) Me2 ab1(46), Me3 ab1(13) Me1 ab2(61), Me2 ab2(18), Me3 ab2(7) Me2 ab2(47), Me1 ab2(25), Me3 ab2(17) Me3 ab1(46), Me2 ab1(20), Me1 ab1(10) Me1 ab1(60), Me3 ab1(14) Me3 sb(26), Me2 sb(20) Me2 sb(30), H11C3 in-plane b(22), Me3 sb(9) Me1 sb(44), H11C3 in-plane b(14), Me3 sb(10) H11C3 in-plane b(40), Me3 sb(18), Me2 sb(17) Me3 r1(30), Me1 r1(24), Me2 r1(14) Me1 r1(28), H11C3 in-plane b(22), Me2 r1(11) Me3 r1(36), Me2 r2(35) Me2 r1(35), Me3 r1(23), Me1 r1(15) Me1 r2(80), Me2 r2(10) Me2 r2(35), Me3 r1(33), H11C3 out-of-plane(22) C2C1 s(40), C3C2 s(32), C5C4 s(21) C2C3C4 b(38), C3C4C6 b(15) C3C2 s(40), C2C1 s(27), C5C4 s(18), C6C4 s(14) H11C3 out-of-plane(68), Me2 r2(11), Me3 r2(6) C5C4 s(27), C6C4 s(20), C2C1 S(15) O7yC2 in-plane b(65), C2C3C4 b(24) O7yC2 out-of-plane(60), H11C3 out-of-plane(8) C4yC3 out-of-plane(70), O7yC2 out-ofplane(17) C6C4 s(40), C3C2 s(20), C5C4 s(14) C3C4C6 b(38), C1C2C3 b(23), C3C4C5 b(15) C3C4C5 b(26), C1C2C3 b(22), C3C4C6 b(20) C1C2C3 b(26), C3C4C6 b(14), C2C3C4 b(10) Me2 t(34), Me1 t(14), O7yC2 out-of-plane(10) C3C2 t(30), Me2 t(18), Me3 t(16) Me1 t(68), Me3 t(9) Me3 t(52), Me2 t(17), Me1 t(5) C4yC3 t(60), C3C2 t(30)
A0 A0 A0 A0 A 00 A 00 A 00 A0 A0 A0 A0 A0 A 00 A0 A 00 A 00 A0 A0 A0 A0 A0 A0 A0 A0 A 00 A0 A 00 A 00 A0 A0 A0 A 00 A0 A0 A 00 A 00 A0 A0 A0 A 00 A0 A 00 A 00 A 00 A 00
˚. Onsager SCRF Model, a0 4.30 A Frequencies in cm -1. Scaling factor using 0.96, except for * using 0.94. c IR intensity in km mol ⫺1. d See Ref. [8], w weak, m middle, sh shoulder, s strong, v very. e P.E.D. (potential energy distributions): s, stretch; ss, symmetric stretch; as, antisymmetric stretch; b, bend; sb, symmetric bend; ab, antisymmetric bend; r, rock; t, torsion; Me, methyl. f Symmetry species. a
b
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calculations were completed using the Wilson GF method [20]. The potential energy distributions of the vibrational modes are calculated by the normal mode analysis. The calculated and experimental frequencies their intensities, potential energy distributions and symmetry species are given in Table 4. The experimental and calculated IR spectra in the liquid phase are compared in Fig. 2. The ab initio calculated frequencies are usually larger than the corresponding experimental values and contain known systematic errors due to the neglect of anharmonicity and electron correlation [14,21]. Therefore, it is usual to scale frequencies predicted at the B3LYP/6-31G* level including some of the effects of electron correlation by an empirical factor of 0.96 [15,22]. However, for a particular molecule, there are some difference for systematic errors of calculated frequencies of different vibrational modes [23,24]. For 4-methyl-3-penten-2one, we scaled the calculated frequencies at the B3LYP/6-31G* level using the scaling factor of 0.96, except for CH3 and C–H stretching modes using that of 0.94 due to strong effect of anharmonicity [21]. The stable conformer of 4-methyl-3-penten-2-one (see Fig. 1) belongs to Cs point group and 45 normal mode vibrational frequencies span the irreducible representations 28 A 0 ⫹ 17 A 00 . Comparing with the observed ones, the average error of the scaled calculated frequencies of IR spectrum was 10 cm ⫺1. Therefore, the scaled calculated frequencies using the DFT method at the B3LYP/6-3lG* level are in good agreement with the experimental values. In detail, the observed weak IR shoulder peak at 3003 cm ⫺1 is assigned to H11C3 s(91) Me2 as1(8) mode calculated at 2978 cm ⫺1. For the weak IR peaks at 2978, 2939 and 2914 cm ⫺1 are assigned to Me1 as1(99) calculated at 2973 cm ⫺1, Me2 as1(90) H11C3 s(8) mode calculated at 2954 cm ⫺1, and Me2 as2(90) mode calculated at 2920 cm ⫺1, respectively. The observed weak IR shoulder peak at 2855 cm ⫺1 is assigned to Me2 ss(60) Me3 ss(40) mode calculated at 2860 cm ⫺1. The strongest IR peak observed near 1689 cm ⫺1 is assigned to O7yC2 s(62) C4yC3 s(15) Me1 ab1(l5) mode of 1703 cm ⫺1. The next strongest IR peak observed at 1619 cm ⫺1 is assigned to C4yC3 s(47) Me3 ab1(19) Me2 ab1(14) O7yC2 s(11) mode of 1618 cm ⫺1. The observed middle IR peak at
1449 cm ⫺1 and middle IR shoulder peak at 1425 cm ⫺1 are assigned to Me2 ab1(46) Me3 ab1(13) mode calculated at 1457 cm ⫺1 and Me1 ab1(60) Me3 ab1(14) mode calculated at 1436 cm ⫺1, respectively. The observed middle IR peaks at 1380 and 1357 cm ⫺1 are assigned to Me2 sb(30) H11C3 in-plane b(22) Me3 sb(9) mode calculated at 1382 cm ⫺1 and Me1 sb(44) H11C3 in-plane b(14) Me3 sb(10) mode calculated at 1357 cm ⫺1, respectively. The observed middle IR peaks at 1220, 1166 cm ⫺1 and weak IR peak at 1069 cm ⫺1 are assigned to Me3 r1(30) Me1 r1(24) Me2 r1(14) mode of 1209 cm ⫺1, Me1 r1(28) H11C3 inplane b(22) Me2 r1(11) mode of 1155 cm ⫺1, and Me2 r1(35) Me3 r1(23) Me1 r1(15) mode of 1067 cm ⫺1, respectively. The observed weak IR peaks at 1019 and 822 cm ⫺1 are assigned to Me1 r2(80) Me2 r2(10) mode of 1011 cm ⫺1 and H11C3 out of plane(68) Me2 r2(11) Me3 r2(6) mode of 830 cm ⫺1, respectively. The observed middle and weak IR peaks at 965 and 900 cm ⫺1 are assigned to C2C1 s(40) C3C2 s(32) C5C4 s(21) mode of 943 cm ⫺1 and C3C2 s(40) C2C1 s(27) C5C4 s(18) C6C4 s(14) mode of 830 cm ⫺1, respectively. The observed middle and weak IR peaks at 622 and 459 cm ⫺1 are assigned to O7yC2 in-plane b (65) C2C3C4 b (24) mode of 604 cm ⫺1 and C4yC3 out-of-plane(70) O7yC2 out-of-plane(17) mode of 450 cm ⫺1, respectively. In Table 4, each frequency corresponds to a different vibrational mode which is principal in potential energy distributions. Fig. 2 displays the, experimental and calculated IR spectra in the liquid phase. It has shown that calculated peaks are in good agreement with experimental peaks. Note that some calculated peaks getting close to each other cannot be distinguished in the experimental spectra, and some calculated lines of lower intensities are not observed in the experimental spectra. 3.4. The solvent effects on the infrared spectra The shifts of frequencies and changes of IR intensities from the gas phase to medium are listed in Table 5. On going from the gas phase to solutions and liquid phase, shifts of frequencies are nearly same in chlorobenzene and 1,2-dichchloroethane solutions. In the liquid phase, there is small frequency shifts for
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Table 5 Calculated vibrational frequencies for 4-methyl-3-penten-2-one in the gas phase, solutions, and liquid phase a
no.
Gas phase (1 1.0) Freq. (Cal.) e
n1 n2 n3 n4 n5 n6 n7 n8 n9 n10 n11 n12 n13 n14 n15 n16 n17 n18 n19 n20 n21 n22 n23 n24 n25 n26 n27 n28 n29 n30 n31 n32 n33 n34 n35 n36 n37 n38 n39 n40 n41 n42 n43 n44 n45
3204 3168 3155 3132 3101 3082 3072 3045 3037 3029 1777 1690 1536 1518 1505 1503 1497 1494 1443 1438 1413 1404 1257 1201 1122 1110 1053 1019 981 971 921 861 831 629 604 467 441 378 340 215 209 150 112 96 55
Int. (IR) f
Solution b (1 5.708) c Freq. (Cal)
Int. (IR)
(1 10.65) Freq. (Cal)
2.7 14.3 20.7 16.3 13.3 28.3 8.1 3.3 44.4 7.4 110.5 213.4 14.8 35.1 0.4 10.0 5.4 31.4 1.6 22.3 34.2 4.8 45.9 70.0 1.8 13.2 6.3 4.7 51.1 1.6 2.9 7.3 1.0 25.0 0.7 2.8 0.6 2.7 1.6 3.9 0.5 0.1 0.0 0.8 2.8
⫺3 ⫺4 3 4 1 2 1 1 1 1 ⫺4 ⫺5 0 ⫺1 0 0 0 0 1 0 ⫺1 0 1 0 0 0 1 1 1 0 0 1 0 ⫺1 1 1 1 0 0 ⫺1 ⫺1 0 6 5 1
0.6 10.5 ⫺ 1.8 1.1 0.1 ⫺ 0.8 3.2 0.0 5.3 5.7 25.8 80.1 1.2 16.3 0.1 1.5 0.7 12.0 1.8 6.2 6.9 4.4 12.4 28.4 0.4 5.0 1.1 0.7 19.3 1.8 1.8 1.5 0.6 8.1 0.1 0.3 0.1 1.3 0.5 1.7 0.2 0.1 0.1 ⫺ 0.1 0.6
⫺3 ⫺4 3 4 1 2 1 1 1 1 ⫺4 ⫺5 0 ⫺1 0 0 0 0 1 0 ⫺1 0 1 0 0 0 ⫺1 ⫺1 ⫺1 0 0 1 0 0 1 1 1 0 0 ⫺1 ⫺1 0 6 5 1
d
Int. (IR) 0.7 12.4 ⫺ 2.0 1.3 0.0 ⫺ 0.9 3.6 0.0 6.2 6.6 30.4 94.2 1.4 19.3 0.1 1.8 0.8 14.1 2.2 7.3 8.2 5.3 14.6 33.9 0.5 5.9 1.3 0.7 23.1 2.0 2.1 1.7 0.7 9.7 0.1 0.4 0.2 1.6 0.5 2.0 0.2 0.1 0.1 ⫺ 0.1 0.7
˚. Onsager SCRF Model at the B3IYP/6-31G(d) level, a0 4.30A Shifts of frequencies and changes of IR intensities from the gas phase to solutions, or liquid phase. c Solvent (1 5.708) is chlorobenzene. d Solvent (1 10.65) is 1,2-dichloroethane. e Frequence in cm ⫺1. f IR intensity in km mol ⫺1. a
b
Liquid phase b (1 15.4) Freq. (Cal) ⫺3 ⫺4 4 5 1 2 1 1 2 1 ⫺5 ⫺6 0 ⫺2 0 ⫺1 1 0 1 0 ⫺1 0 1 0 0 0 ⫺1 ⫺1 ⫺1 0 1 2 0 ⫺ 1 1 1 1 0 0 ⫺1 ⫺1 0 7 5 1
lnt. (IR) 0.7 13.7 ⫺ 2.5 1.2 0.0 ⫺ 1.2 4.0 0.0 5.7 7.6 31.7 101.2 1.5 20.9 0.2 1.8 1.0 15.2 2.4 7.7 7.8 6.2 15.4 35.6 0.5 6.3 1.3 0.8 24.1 2.3 2.5 1.8 0.8 10.2 0.1 0.4 0.2 1.7 0.6 2.1 0.2 0.1 0.0 ⫺ 0.1 0.7
170
S. Xu et al. / Journal of Molecular Structure (Theochem) 459 (1999) 163–170
n1, n2, n3, n4, n11, n12, n43 and n44. Where, n1 and n2 are Me3 antisymmetric stretching and C–H stretching vibrations, red shifts about 3–4 cm ⫺1; n11 and n12 are mixed modes of O7yC2 and C4yC3 stretching vibrations, red shifts about 5–6 cm ⫺1. However, n3 and n4 are Me1 and Me2 antisymmetric stretching vibrations, blue shifts about 4–5 cm ⫺1; n43 and n44 are methyl torsion modes, blue shifts about 5–7 cm ⫺1. In general, on going from the gas phase to liquid phase, most absorption peaks become sronger, where the strong IR peaks in the gas phase become much stronger in medium. For instance, significant changes of IR intensities are observed in n11, n12, n14, n24, n29, where, n12 of C4yC3 and O7yC2 mixed mode has the largest changes in intensities (up to 101 km mol ⫺1 in the liquid phase). 4. Conclusions We have found mesityl oxide has a stable conformation of s-cis, the optinmized geometry is in good agreement with the experimental data. On going from the gas phase to solutions and liquid phase, the solvent reaction field has general weak influence on the skeletal bond angles, dipole moment, and thermodynamics properties of the molecule. The scaled calculated frequencies using the Onsager SCRF model at the B31YP/6-31G* level are all in good agreement with the experimental values. The infrared spectrum of the molecule is weak influenced by the solvent reaction field. Specially, for the two main bands of CyC and CyO mixed vibrational modes, small frequency shifts (5–6 cm ⫺1), but relatively large changes of intensities (up to 101 km mol ⫺1 in the liquid phase) are found.
Acknowledgements This work was supported in part by grants from the National Science Foundation of China and State Key Laboratory of Short Wavelength Chemical Lasers.
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