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Studies of hydrogen bonding1
OElsevier Scientific Publishing Company, Amsterdam -Printed
in The Netherlands
Short communication
STUDIES OF HYDROGEN Part XX-X. Cyclohexyl
T. GRAMSTAD Department
BONDING*
isocyanide
as proton acceptor in hydrogen bonding
and K. TJESSEM
of Chemistry,
University
of Bergen,
N-5014
Bergen-Univ.
(Norway)
(Received 6 October 1977)
In a previous publication [l] it was shown, by studying the association of phenol with nitriles, that the phenol O--f-I proton in the complex was located perpendicular to the triple bond. As a logical extension of this work the system phenol/cyclohexyl isocyanide was examined with the purpose of examining the hydrogen bonding site to the -N’=Cgroup. EXPERIMENTAL
Cyclohexyl isocyanide was redistilled at reduced pressure in an atmosphere of nitrogen immediately before use. E’urification of phenol and carbon tetrachloride, the methods of evaluation of association constants and dipole moments, and the CNDO/2 calculations were the same as reported in detail elsewhere [l-3]. The polarization data OL,p, y, Poe,R, and the experimental dipole moments of the isocyanide and of the hydrogen-bonded complex, C6HSOH/C6HIINC, are given in Table 1. The Avon value for the interaction of phenol with cyclohexyl &cyanide was found to be 250 cm-‘. Furthermore, in the Tables 2 and 3 we have presented CND0/2 calculations of the dipole and of the corresponding total energies, E, of various types moments, ~~~~~~~ of planar C6H50H/C6H11NC complexes when phenol O-H is located perpendicular to and along the triple bond. Calculations of dipole moments of various types of out-of-plane models gave unfavourable total energies. The gross orbital charges on different atoms in cyclohexyl isocyanide, in phenol, and in the most stable C,H50H/C,H, ,NC structure have been tabulated in Table 4. RESULTS AND DISCUSSION
Allerhand and Schleyer [4] concluded from a study of the system C,H,OH/ RNC that the most probable hydrogen bonding site was to the C atom in the *For Part XXIX
see ref. 1.
148
TABLE 1 ExperimentaI, flexp, and CNDO/S calcuIated, orcaic dipole moments, total polarization, molar refraction,RD, and the parameters LY,p &d 7 for cyclohexyl isocyanide and for the hydrogen-bonded complex with phenol
P,,
a C,H, PC C,H,OH/C,H,
,NC
P
P,
7
35.997
0.2889
-0.02357
63.225
0.3561
-0.0697
%alculated at energy minimum (E = -69.2367 bCalculated at energy minimum (E = -134.5719
RD
P'"~(D)
p-l=(D)
440.40
24.59
4.49
4.59a
1402.75
52.68
8.07
7.96b
a.u.). a-u.).
TABLE 2 CND0/2 calculated dipole moments, ~~~~~~~and total energies, E, of the planar hydrogenbonded complex as a function of the distances d ands. The -N+=C-(X16.4) is kept constant
s = 1.05 # d
s = 1.07 f% CdC
p’x
E
@I
iD)
(a-u.)
2.30 2.35 2.40 2-45 2.50 2.55 2.60 2.65 2.70 2.75 2.80
5.25 5.12 5.00 4-88 4.76 4.63 4.44 4.39 4.35 4.26 4.19
-134.5392 -134.5487 -134.5550 -134-5595 -134.5624 -134.5645= -134.5643 -134.5640 -134.5635 -134.5624 -134.5610
talc
d = 2.55 JI
E
s
(D)
(a-u.)
(A)
;;;>
5.41 5.28 5.14 5.01 4.88 4.76 4.63 4.40 4.36 4.32 4.25
-134.5365 -134.5468 -134.5538. -134-5586 -134.5618 -134.5635= -134.5630 -134.5629 -134.5625 -134.5620 -134.5605
1.00
4.43 4.46 4.51 4-52 4.56 4.63 4.70 4.76 4.81
PX
1.01 1.02 l-03 1.04 1.05 1.06 1.07 1.08
CalC
E
(a.u.) -134.5592
-134.5609 -134.5623 -134-5632 -134.5637 -134.5645= -134.5639 -134.5 635 --134.5629
=E, minimum. group. Our study of the C6H50H/C6HllNC complex confirms their proposal. We found the experimental dipole moment, pXexP,to be 8.07 D whereas CNDO/Z calculations gave a dipole moment of 4.63 D for the complex when the phenol O-H proton was located perpendicular to, and ‘i-96 D when it was acting along, the triple bond (see Tables 2 and 3). These findings leave no doubt that the phenol O-H proton is located along the triple bond in the -N+=C- group. By comparison of gross orbital charges on different atoms before and after complexation (see Table 4), we can see that there is, as for the system
-N+=C-
TABLE3 Thesame comparisonasinTable 2,butthe phenolo-Hproton triple bond
islocatedalongthe
5 PHs ---H-O ~__-____--_-
+ C6H,, N-_-C-
d
s= 1.05 A d
talc KS
(A)
(D)
2.30 2.35 2.40 2.45 2.50 2.55 2.60 2.65 2.70 2.75 2.80 2.85
8.77 8.55 8.35 8.15 7.96 7.78 7.61 7.45 7.29 7.15 7.02 6.90
s= 1.07 a
B (a-u.) -134.5520 -134.5602 -134.5657 -134.5691 -134.5709 -134.5714= -134.5710 -134.5699 -134.5683 -134.5665 -134.5645 -134.5624
talc
k (D) 9.04
8.81 8.58 8.37 8.16 7.96 7.77 7.60 7.43 7.27 7.13 6-99
d =
2.55 A
E
s
E
(au.)
(A)
(au.)
-134.5507 -134.5597 -134.5657 -134.5694 -134.5713 -134.5719= -134.5715 -134.5703 -134.5686 -134.5667 -134.5645 -134.5622
1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.15
7.40 7.47 7.54 7.62 7.70 7.78 7.87 7.96 8.05 8.15 8.26 8.84
-134.5645 -134.5666 -134.5683 -134.5697 -134.5707 -134.5714 -134.5718 -134.5719= -134.5717 -134.5714 -134.5708 -134.5648
CsHSOH/CHSCN [ 11, a considerable charge redistribution in both interacting molecules. AlI the atoms in the proton acceptor part of the complex, except C14, decrease their total charge, gt, whereas the atoms in the proton donor part, with the exception of C’ and H8 increase their charge. The interference is greater in those atoms which are directly involved in the H-bond, e-g_ on complexation the H8, Cg and N lo atoms lose electron densities, t0.0452, +0.0385 and +0.0284 e, respectively, whereas the 0’ atom gains electron density, -6.0471 e. By summing [l] the net charges (e.g., the net charges on H’, 0’ and N’O are +0.2093, -0.3586 and +0.0009 e) on the various atoms in the complex, the charge transfer, CT, from cyclohexyl isocyanide to phenol was found to be 0.1040 e. Most of this charge transfer comes from the Cg and N” atoms (0.0664 e). For comparison, the charge transfer of the system C6HSOH/CH,CN was found [l] to be 0.0558 e. By using an equation outlined by Bonchev and Cremaschi [5] the total charge shift, TCS, of the C6H50H/C6H1 INC complex and the charge shifts within the proton donor, C&, and the acceptor part, CS,, of the complex, were found to be 0.0491,0.0476 and 0.0015 e, respectively. The corresponding values for the system C6HSOH/CH&N were CS, = 0.0256, CS, = 0.0042 and TCS = 0.0298 e [l]. These results show, as for the system C6HSOH/CH& [ 1], that the proton acceptor molecule causes more charge redistribution on the proton donor than the proton donor in the acceptor. The reason for this,
150 TABLE4 CNn0/2 calculatedgrossorbitalchagesondifferentatomsincycloheKylisocyanide, phenolandinthe cycfohexylisocyanide/phenolcomplex.(E=-134.5719a.u.)
2s
0.9930 0.9888 C3 0.9836 C' O-9847 C5 0.9621 C6 0.9838 0' 1.5729 C9 1.6718 N'" 1.2912 C" 0.9371 C'Z 0.9525 C!'" 0.9394 C 14 0.9593 C'S 0.9554 C'6 0.9605
2PX
2PY
2Pz
Qt
0.8351 1.0312 0.9472 3.8065 1.0159 0.9921 1.0601 4.0569 1.0213
1.0054
0.9730
0.9880 1.0092 1.0241 l-2789 1.0939 1.1125 0.8740 1.0377 1.0205 1.0103 1.0188 1.0238
1.0168 1.0193 0.9964 1.4997 0.6948 1.3101 1.0412 1.0216 1.0260 1.0172 1.0392 1.0013
1.0448 4.0343 0.9731 3.9837 1.0686 4.0711
3.9832
1.9332
6.2845
0.6902 1.3137 1.0364 0.9986 1.0140 0.9950 0.9799 1.0163
4.1507 5.0275 3.8887 4.0104 3.9998 3.9818 3.9933 4.0020
lsHZ(0.9824),H3 (0.9915),H4 (0.9976) lsHS(0.9899),H6 (0.9825),H'(0.8359) 1s H" (0.9998),H" (0.976"-,1.0045) 1s HI3 (0.9823,1.0142),H'4(0.9963, 1.0146),H*5 (0.9827,0.9988) lsH'"(0.9907,0.9854)
2s 0.9962 0.9895 0.9847 0.9832 0.9831 0.9841 - 1.6557 1.6118 1.3024 0.9398 0.9523 0.9391 0.9593 0.9552 0.9604
2PX
2PY
2Pz
qt
0.9686 1.0136 0.9874 1.0054 1.0414 0.9939 1.2936 1.0566 1.1256 0.8507 1.0425 1.0146 1.0121 1.0132 1.0277
0.9182 1.0466 0.9941 1.0418 0.9778 1.0641 1.7814 0.7247 1.2834 1.0523 1.0136 1.0288 1.0158 1.0415 1.0010
0.9211 1.0184 1.0186 1.0164 0.9832 1.0424 1.6278 0.7191 1.2877 1.0444 1.0014 1.0163 0.9956 0.9828 1.0121
3.8041 4.0680 3.9848 4.0468 3.9855 4.0846 6.3536 4.1122 4.9991 3.8872 4.0098 3.9988 3.9828 3.9927 4.0013
H2(0.9889),H3 (0.9989),H4(1.0044) H5 (0.9981),H6 (0.9906),H'(0.7907) H"(0.9969),H'=(0.9740,1.0022) H'"(0.9792,1.0117),H'4 (0.9929, 1.0120),H'5(0.9795,0.9960) H'6(0.9880,0.9798)
we believe,isthe greater electron mobilitywithinthe phenolmoleculethan withintheacetonitrile andisocyanide molecule. Theresultsalso show clearly thattheelectronredistributionisgreater within acetonitrile(CS, = 0.0042 e) thanwithin cyclohexylisocyanidemolecule (CS,=O.O015 e),in spiteofthe
fact that cyclohexyl isocyanide forms the stronger H-bond. On the contrary, however, cycbhexyl isocyanide causes, as expected from the H-bond strength, much more charge shift in phenol (0.00476 e) than does acetonitrile (0.0256 e). In this connection it should be noted that we are dealing with two different types of H-bonding, X-H - - - 5~ electrons in the system CsH50H/CH3CN and X-H.__ n electrons in C6H50H/C6HIINC. Kollman and Allen [6] have indicated that the charge shift is a more important physical effect than charge transfer for moderate and weak H-bonds. However, in the two systems, C6HSOH/CH3CN (Avon = 160 cm-‘) [l] and CsHsOH/CsHIINC (A Von = 250 cm-‘), we have studied, the charge transfer (0.0558 and 0.1040 e), dominates over the charge shift (0.0298 and 0.0491 e).
151 REFERENCES 1 2 3 4 5 6
T. T. T. A. D. P.
Gramstad and K. Tjessem, J. Mol. Struct., 41 (1977) 231. Gramstad and K. Tjessem, Acta ChBm. Stand. Part B, 31 (1977) 345. Gramstad and 0. R. Simonsen, Spectrochim. Acta Part A, 32 (1976) 723. Allerhand and P. V. R. Schleyer, J. Am. Chem. Sot., 85 (1963) 866. Bonchev and P. Cremaschi, Theor. Chim. Acta, 35 (1974) 69. A. Kollman and L. C_ Allen, J_ Am_ Chem. Sot., 93 (1971) 4991.
in The Netherlands
Short communication
STUDIES OF HYDROGEN Part XX-X. Cyclohexyl
T. GRAMSTAD Department
BONDING*
isocyanide
as proton acceptor in hydrogen bonding
and K. TJESSEM
of Chemistry,
University
of Bergen,
N-5014
Bergen-Univ.
(Norway)
(Received 6 October 1977)
In a previous publication [l] it was shown, by studying the association of phenol with nitriles, that the phenol O--f-I proton in the complex was located perpendicular to the triple bond. As a logical extension of this work the system phenol/cyclohexyl isocyanide was examined with the purpose of examining the hydrogen bonding site to the -N’=Cgroup. EXPERIMENTAL
Cyclohexyl isocyanide was redistilled at reduced pressure in an atmosphere of nitrogen immediately before use. E’urification of phenol and carbon tetrachloride, the methods of evaluation of association constants and dipole moments, and the CNDO/2 calculations were the same as reported in detail elsewhere [l-3]. The polarization data OL,p, y, Poe,R, and the experimental dipole moments of the isocyanide and of the hydrogen-bonded complex, C6HSOH/C6HIINC, are given in Table 1. The Avon value for the interaction of phenol with cyclohexyl &cyanide was found to be 250 cm-‘. Furthermore, in the Tables 2 and 3 we have presented CND0/2 calculations of the dipole and of the corresponding total energies, E, of various types moments, ~~~~~~~ of planar C6H50H/C6H11NC complexes when phenol O-H is located perpendicular to and along the triple bond. Calculations of dipole moments of various types of out-of-plane models gave unfavourable total energies. The gross orbital charges on different atoms in cyclohexyl isocyanide, in phenol, and in the most stable C,H50H/C,H, ,NC structure have been tabulated in Table 4. RESULTS AND DISCUSSION
Allerhand and Schleyer [4] concluded from a study of the system C,H,OH/ RNC that the most probable hydrogen bonding site was to the C atom in the *For Part XXIX
see ref. 1.
148
TABLE 1 ExperimentaI, flexp, and CNDO/S calcuIated, orcaic dipole moments, total polarization, molar refraction,RD, and the parameters LY,p &d 7 for cyclohexyl isocyanide and for the hydrogen-bonded complex with phenol
P,,
a C,H, PC C,H,OH/C,H,
,NC
P
P,
7
35.997
0.2889
-0.02357
63.225
0.3561
-0.0697
%alculated at energy minimum (E = -69.2367 bCalculated at energy minimum (E = -134.5719
RD
P'"~(D)
p-l=(D)
440.40
24.59
4.49
4.59a
1402.75
52.68
8.07
7.96b
a.u.). a-u.).
TABLE 2 CND0/2 calculated dipole moments, ~~~~~~~and total energies, E, of the planar hydrogenbonded complex as a function of the distances d ands. The -N+=C-(X16.4) is kept constant
s = 1.05 # d
s = 1.07 f% CdC
p’x
E
@I
iD)
(a-u.)
2.30 2.35 2.40 2-45 2.50 2.55 2.60 2.65 2.70 2.75 2.80
5.25 5.12 5.00 4-88 4.76 4.63 4.44 4.39 4.35 4.26 4.19
-134.5392 -134.5487 -134.5550 -134-5595 -134.5624 -134.5645= -134.5643 -134.5640 -134.5635 -134.5624 -134.5610
talc
d = 2.55 JI
E
s
(D)
(a-u.)
(A)
;;;>
5.41 5.28 5.14 5.01 4.88 4.76 4.63 4.40 4.36 4.32 4.25
-134.5365 -134.5468 -134.5538. -134-5586 -134.5618 -134.5635= -134.5630 -134.5629 -134.5625 -134.5620 -134.5605
1.00
4.43 4.46 4.51 4-52 4.56 4.63 4.70 4.76 4.81
PX
1.01 1.02 l-03 1.04 1.05 1.06 1.07 1.08
CalC
E
(a.u.) -134.5592
-134.5609 -134.5623 -134-5632 -134.5637 -134.5645= -134.5639 -134.5 635 --134.5629
=E, minimum. group. Our study of the C6H50H/C6HllNC complex confirms their proposal. We found the experimental dipole moment, pXexP,to be 8.07 D whereas CNDO/Z calculations gave a dipole moment of 4.63 D for the complex when the phenol O-H proton was located perpendicular to, and ‘i-96 D when it was acting along, the triple bond (see Tables 2 and 3). These findings leave no doubt that the phenol O-H proton is located along the triple bond in the -N+=C- group. By comparison of gross orbital charges on different atoms before and after complexation (see Table 4), we can see that there is, as for the system
-N+=C-
TABLE3 Thesame comparisonasinTable 2,butthe phenolo-Hproton triple bond
islocatedalongthe
5 PHs ---H-O ~__-____--_-
+ C6H,, N-_-C-
d
s= 1.05 A d
talc KS
(A)
(D)
2.30 2.35 2.40 2.45 2.50 2.55 2.60 2.65 2.70 2.75 2.80 2.85
8.77 8.55 8.35 8.15 7.96 7.78 7.61 7.45 7.29 7.15 7.02 6.90
s= 1.07 a
B (a-u.) -134.5520 -134.5602 -134.5657 -134.5691 -134.5709 -134.5714= -134.5710 -134.5699 -134.5683 -134.5665 -134.5645 -134.5624
talc
k (D) 9.04
8.81 8.58 8.37 8.16 7.96 7.77 7.60 7.43 7.27 7.13 6-99
d =
2.55 A
E
s
E
(au.)
(A)
(au.)
-134.5507 -134.5597 -134.5657 -134.5694 -134.5713 -134.5719= -134.5715 -134.5703 -134.5686 -134.5667 -134.5645 -134.5622
1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.15
7.40 7.47 7.54 7.62 7.70 7.78 7.87 7.96 8.05 8.15 8.26 8.84
-134.5645 -134.5666 -134.5683 -134.5697 -134.5707 -134.5714 -134.5718 -134.5719= -134.5717 -134.5714 -134.5708 -134.5648
CsHSOH/CHSCN [ 11, a considerable charge redistribution in both interacting molecules. AlI the atoms in the proton acceptor part of the complex, except C14, decrease their total charge, gt, whereas the atoms in the proton donor part, with the exception of C’ and H8 increase their charge. The interference is greater in those atoms which are directly involved in the H-bond, e-g_ on complexation the H8, Cg and N lo atoms lose electron densities, t0.0452, +0.0385 and +0.0284 e, respectively, whereas the 0’ atom gains electron density, -6.0471 e. By summing [l] the net charges (e.g., the net charges on H’, 0’ and N’O are +0.2093, -0.3586 and +0.0009 e) on the various atoms in the complex, the charge transfer, CT, from cyclohexyl isocyanide to phenol was found to be 0.1040 e. Most of this charge transfer comes from the Cg and N” atoms (0.0664 e). For comparison, the charge transfer of the system C6HSOH/CH,CN was found [l] to be 0.0558 e. By using an equation outlined by Bonchev and Cremaschi [5] the total charge shift, TCS, of the C6H50H/C6H1 INC complex and the charge shifts within the proton donor, C&, and the acceptor part, CS,, of the complex, were found to be 0.0491,0.0476 and 0.0015 e, respectively. The corresponding values for the system C6HSOH/CH&N were CS, = 0.0256, CS, = 0.0042 and TCS = 0.0298 e [l]. These results show, as for the system C6HSOH/CH& [ 1], that the proton acceptor molecule causes more charge redistribution on the proton donor than the proton donor in the acceptor. The reason for this,
150 TABLE4 CNn0/2 calculatedgrossorbitalchagesondifferentatomsincycloheKylisocyanide, phenolandinthe cycfohexylisocyanide/phenolcomplex.(E=-134.5719a.u.)
2s
0.9930 0.9888 C3 0.9836 C' O-9847 C5 0.9621 C6 0.9838 0' 1.5729 C9 1.6718 N'" 1.2912 C" 0.9371 C'Z 0.9525 C!'" 0.9394 C 14 0.9593 C'S 0.9554 C'6 0.9605
2PX
2PY
2Pz
Qt
0.8351 1.0312 0.9472 3.8065 1.0159 0.9921 1.0601 4.0569 1.0213
1.0054
0.9730
0.9880 1.0092 1.0241 l-2789 1.0939 1.1125 0.8740 1.0377 1.0205 1.0103 1.0188 1.0238
1.0168 1.0193 0.9964 1.4997 0.6948 1.3101 1.0412 1.0216 1.0260 1.0172 1.0392 1.0013
1.0448 4.0343 0.9731 3.9837 1.0686 4.0711
3.9832
1.9332
6.2845
0.6902 1.3137 1.0364 0.9986 1.0140 0.9950 0.9799 1.0163
4.1507 5.0275 3.8887 4.0104 3.9998 3.9818 3.9933 4.0020
lsHZ(0.9824),H3 (0.9915),H4 (0.9976) lsHS(0.9899),H6 (0.9825),H'(0.8359) 1s H" (0.9998),H" (0.976"-,1.0045) 1s HI3 (0.9823,1.0142),H'4(0.9963, 1.0146),H*5 (0.9827,0.9988) lsH'"(0.9907,0.9854)
2s 0.9962 0.9895 0.9847 0.9832 0.9831 0.9841 - 1.6557 1.6118 1.3024 0.9398 0.9523 0.9391 0.9593 0.9552 0.9604
2PX
2PY
2Pz
qt
0.9686 1.0136 0.9874 1.0054 1.0414 0.9939 1.2936 1.0566 1.1256 0.8507 1.0425 1.0146 1.0121 1.0132 1.0277
0.9182 1.0466 0.9941 1.0418 0.9778 1.0641 1.7814 0.7247 1.2834 1.0523 1.0136 1.0288 1.0158 1.0415 1.0010
0.9211 1.0184 1.0186 1.0164 0.9832 1.0424 1.6278 0.7191 1.2877 1.0444 1.0014 1.0163 0.9956 0.9828 1.0121
3.8041 4.0680 3.9848 4.0468 3.9855 4.0846 6.3536 4.1122 4.9991 3.8872 4.0098 3.9988 3.9828 3.9927 4.0013
H2(0.9889),H3 (0.9989),H4(1.0044) H5 (0.9981),H6 (0.9906),H'(0.7907) H"(0.9969),H'=(0.9740,1.0022) H'"(0.9792,1.0117),H'4 (0.9929, 1.0120),H'5(0.9795,0.9960) H'6(0.9880,0.9798)
we believe,isthe greater electron mobilitywithinthe phenolmoleculethan withintheacetonitrile andisocyanide molecule. Theresultsalso show clearly thattheelectronredistributionisgreater within acetonitrile(CS, = 0.0042 e) thanwithin cyclohexylisocyanidemolecule (CS,=O.O015 e),in spiteofthe
fact that cyclohexyl isocyanide forms the stronger H-bond. On the contrary, however, cycbhexyl isocyanide causes, as expected from the H-bond strength, much more charge shift in phenol (0.00476 e) than does acetonitrile (0.0256 e). In this connection it should be noted that we are dealing with two different types of H-bonding, X-H - - - 5~ electrons in the system CsH50H/CH3CN and X-H.__ n electrons in C6H50H/C6HIINC. Kollman and Allen [6] have indicated that the charge shift is a more important physical effect than charge transfer for moderate and weak H-bonds. However, in the two systems, C6HSOH/CH3CN (Avon = 160 cm-‘) [l] and CsHsOH/CsHIINC (A Von = 250 cm-‘), we have studied, the charge transfer (0.0558 and 0.1040 e), dominates over the charge shift (0.0298 and 0.0491 e).
151 REFERENCES 1 2 3 4 5 6
T. T. T. A. D. P.
Gramstad and K. Tjessem, J. Mol. Struct., 41 (1977) 231. Gramstad and K. Tjessem, Acta ChBm. Stand. Part B, 31 (1977) 345. Gramstad and 0. R. Simonsen, Spectrochim. Acta Part A, 32 (1976) 723. Allerhand and P. V. R. Schleyer, J. Am. Chem. Sot., 85 (1963) 866. Bonchev and P. Cremaschi, Theor. Chim. Acta, 35 (1974) 69. A. Kollman and L. C_ Allen, J_ Am_ Chem. Sot., 93 (1971) 4991.