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Intra- and inter-molecular vibrations of a hydrogen bond system
Volume 13; numti
2
CHEMICAL PHYSICS LETTERS
._. .' '. .. .: . ..: 2 .'. .,, ;. ..,_ '. .. ,' _ '...,,'. ', :. .._ ...._'. : .~NTRA-ANDINTER-MOLECULAR'VIBRATIQNS
15 Febky
..I '. .I
,.
'. ._ t ,' AI
..
.' ..
1972
OF AHYDROC+~B*N~~~Y~~E~~
P:V. HUONG:and A. GRAJA * .&a&orafoirede Sperrrormpie Infrarouge. associe’au C&_R.S.: ,Universir& de Bordeaux I. 33-Talence. France
AlI the intermolecular
.’
;
viirations of an isolated hydrogen bond are observed for the first time, with the phenol-
mathylpyridinoxide complex in dilute solution in quasi-inert solvents. The spectral characteristics obtained are anaIysPd by comparison with thos: of the intramoIecu?ar vibrations of the c~emi~igroups dire&y involved in the hp drogen bond, C-0-H...O-?I. The latter is found to be relatively strong and proiokes’a reduction by 2OF of the stretching frequency ~f0Hf and an increase by 200% of the out-of-plane deformation’T(OH) and by 2% of the in-
plane bending 6(OH). It provokesalso the appearance of the intermolecular stretching of001 at 194 cm’*_ the intermoiecutar
out-f-plane
twisting ~(00)
at 324 ~-II-~, and two in-plane 00
1. Introduction The expansion of low frequency spectroscopy in recent years has allowed the study of iotermoleculai vibrations
of the hydrogen
bond.
Nevertheless,
bending modes at 78 and 135 cm-*.
terferonieter RiIC coupled with a digital-analys& FTC f00-7-giving directly the intensity spectrkm versus the frequency from 20 to 400 cm-l.
one
notices that the chemical systems examined are rarely those of which intramolecular vibrations have been pteviousiy determined by studies in the near- and midinfrared regions. In addition to this, these works were frequently done with solid samples; and: a$ is we:1 known, in t&is physicalstate not only the hydrogen’ bond X-H...Y, but also chain mul~~ers can exist [l--S] i or a great number.of moleiules can be found in the same unit cell [6]. The dilute soiution of the. complex in an inert soIvent could present the advantage of offering an isolated hydrogen bond [7-g]. Hqwever; the rare works thai.have beeri done in the low frequency region were restricted solely to the stretching a(XY) [7,8]. 1. :,‘. We have examined, in the liquid,phase, a great. number df hydrogen bonded complexeS in quasi-inert. soltients, on +wide frequency-range, ffijrn 4000’tp 20,
2. Results
and discussion
Under the influence of the hydrogen bonding, the vibrations r&It&g from the phenolic and pyridinic rings are slightly
affected;
On the contrary,
those C.&r-
responding to the groups C-O-H of phenol and N-O of py~d~oxide are very strongly modified. We note effectively an important reduction, by 20%, of the stretching frequency b(OH), the spectral profile showing’many sub-maxima (fig. l), and’an incre,asirfg of the out-of-plane deformation r(OH) and of the in: plane bending S(OH) frequencies &pectively by. 20% and.256. The v(CO’j stretching frequency is also :j fdund to be incieased (table- I). We must mention ‘1’
that although these general spectial modifications
‘.’ z
have be& currently’exp&ted f9-12]., one’can &rely ? find them wiih the gne proton donor: As to the ,T[: v(QN), frequency itself,.a lo+ering qf about 50 cm-l .<. .; ;,.-. is-observed. ,‘;
~Ohme L3, number 2
CHEMICALPtiSICS
15.February
LETTERS
.1972,
The spectrum recorded in the low frequency Te&on shows, for the C6HSOH...0NC,H4CI$3 syst+n .. in dilute solution in carbon disulphide, three intense bands at 324,194 and 78 cm-l and a weak absorp--tion at 135 cm- 1 (fig. 2). The Grst band does,nct correspond’to the phenol bending -f(OH). This latter
has been identified in free phenol tit 315 [IO] and is shifted to 825 cm;1 inpresence of the o’rganic base. The’ identification is also confirmed by the deuterium-hydrogen substitution (table 1). The new bands are due, in consequence, to inter-. molecular vibratory modes. One of.the simplest methods of assignment of the
new absorptions consist of consideringrihe molecular complex as a polyatomic entity containing two point
Fig. 1. Infrared spectrum of phenol-methylpyridinoxide complex in CCL,. Concentration in phenol: 0.01 mole/l; concentration in pyridinoxide: 0.005 mole/i,cell thickness: 0.5 cm.
masses centered at the atoms C of phenol and-N of the organic base gnd to keep intact the other atoms,
involved directly in the hydrogen bond. This superC-OLH...O-N, of the maximum symmetry C, and composed with 5 atoms, has then nine vimolecule;
brations with 7 A’ (in-plane) and 2 A” (ok-of-plane): We can enumerate easily the five imiamolecular vibrations
(table
-41,: W;;,
0.01 mole/l, cell thickness:
Vibrational
(cm-‘)
0.2 cm.
Table
frequencies
WO),
1
of C-O-H and C-O-D groups of PhenolsCeHsOH and C,&OD pyridinoxide in dilute solution in CC& and in CS2
C6H50H Vibrations
with Cmethyl-
bonded
free
bonded
-2
cc14
(32
cc14
cs2
cc14
-2
3610
3593
307s
3060
2665
265.5
1341 311 1177
1340 314 1176
1385 c) 1244 c)
1380 825 1243
1025 ., 254 916
1024 2.55 919
2340 107.5 618 932
1074 617.. 929
1227
1226
dOHI ‘smj) rKW 7(CO)
a) Stretchiig
free and bonded
%%?D
free cc14
Ye)
@N);
The other four vibrations are intermolecular; they can be represented schematically in fig. 3. These oscillatory modes are to be compared with those existing in solid-methanol; the analysis of these latter modes is done very recently [3,4]. The com-
Fin. 2. Far-infrared spectrum of phenol-methylpyridinoxide complex in CS2. Concentration & phenol: 0.1 iolejl; concentration in pyridinoxide:
WH),
1):
:
.I260
1261 1245b)
no7b) .:
frequency o(ON) of methylpyridinoxide.
CC!~, these vibrations
appear respectively
:
‘_ . .
,1243 b)
12oyb)
b) In C!H3N07 ‘z solvent. c) With $e phenol-pyridine ,_ -. ‘. :,.. . :. ,, ,‘. ‘. ._.I ;. ._ ‘. ; ‘.” ...’ ./
._,’
-. complex
diluted p
:
at 1380 and at 1239 cm;*.
I ,.
:
:
::
. ‘.:. ,163’., ,‘.‘; ;_
Volu&i3,
number 2.
15 February 1972
CHEMICALPHYSICSLETTERS
.-
:
I?4 PLANE
-R
iO0)
(RI
)
(A')
IN PIANE RESDISC;
:)UT OF PIAXE DEFORMATION
Fig. 3. Intermolecular
(00)
TtiISTlNG
vibrarions (schematic) hydrogen bond.
of an isolated
A&nowIedgement
garison of the geometrical structure and the intermolecular vibrations of the two systems can help in the assignment of our spectrum. It is easy to identify the 00 sfrerch!ng, o(OO), to the absorption situated at 194 cm-l for the complex dissolved. in carbon disulphide. In a less active solv&it, like carbon tetrachloride [9], this vibration appears at 188 cm-l. This shift is coherent with the fact.that the OH stretching frequency, v(OH), is higher in the latter solvent than in carbon disulphide. This result confirms that for X-H.._Y hydrogen bonds, the stretching o(XY) frequency increases when the stretching v(XH) frequency decreases [ 1 I] . In our complex, tlie our-of-plane 00 defonnariurz, n(OO), that may be compared with the similar motion which appears at 348 cm- 1 in solid a-methanol [4], would be, with the minimllm doubt, the origin of the absorption situated at 324 cm-l. The last bands are due in consequence to the two in-plane-bending motions (COO) and,(OON) of the complex. One,must notice that in a hydrogen bonded system W-O-H...O-2
wheie
in pha& ancj of oppoiite phase. The latter mode can’ be assimilated to an 00 twisting, ~(00) and would app&r at a higher frequency than the former. Inthe &H50H...0NC5HqCH3 complex, the 00 bending which is the most similar to this latter motion is the OON bending; we call it the in-plane 00 twisting, T(OO).. It appears at 135 cm-l. The last absorption at 78 cm-l can then be assigned to the 00 bending mode, /3(00).
W = 2, because
the ex-
istence of a pseudo symmetry center, the two described motioqs must combine one with the other to give rise to two 00 bending m&ions in which the displacement of the two oxygen atoms is respectively
The authors are grateful to Professor J. Lascombe for helpful discussions.
References [I] R.J. Jakobscn and J.W. Brasch, Spectrochim. (1965)
Acta 21
1753.
[2] R.J. Jakobsen, J.W. Brasch and Y. Mikawa, Appl. Spectry. 22 (1968) 641. 131 A.B. Dempster and G. Zerbi, J. Chem. Phys. 54 (1971)
3600. [4] P.T.T. Wang and E. Whalley. J.Chem. Phys. SS (1971) 1830. [S] K. Ito and T. Shimanouchi, Biopolymers 5 (1967) 921. [6] R. Foglizzo and A. Novak, J. Chcm. Phys. 50 (1969) 5366. [7]
S.G.W.
Ginn and’J.i.
Wood,
Spectsochim.
Acta 23A
(1967) 621. [8)
G. Lichtfus and T. Zeegers-Huyskens,J. Mol. Struct. 9 (1971) 343.
[91 P.V. Huong and J.C. Lassegues, Spectrochim. Acta 26A (1970) 269.
[lo] P-V. Huong, M. Couzi and J. Lascombe, J. Chim. Phys. 64 (1967) 1056. [ 111 P.V. Huong and G. Turreli, J. Mol. Spectry. 25 (1968) 185.
[ 121 S. Yon-Bo and V.hi. Chulanovskii, 2 (1963) 218.
Opt. i Spektroskopiya,
2
CHEMICAL PHYSICS LETTERS
._. .' '. .. .: . ..: 2 .'. .,, ;. ..,_ '. .. ,' _ '...,,'. ', :. .._ ...._'. : .~NTRA-ANDINTER-MOLECULAR'VIBRATIQNS
15 Febky
..I '. .I
,.
'. ._ t ,' AI
..
.' ..
1972
OF AHYDROC+~B*N~~~Y~~E~~
P:V. HUONG:and A. GRAJA * .&a&orafoirede Sperrrormpie Infrarouge. associe’au C&_R.S.: ,Universir& de Bordeaux I. 33-Talence. France
AlI the intermolecular
.’
;
viirations of an isolated hydrogen bond are observed for the first time, with the phenol-
mathylpyridinoxide complex in dilute solution in quasi-inert solvents. The spectral characteristics obtained are anaIysPd by comparison with thos: of the intramoIecu?ar vibrations of the c~emi~igroups dire&y involved in the hp drogen bond, C-0-H...O-?I. The latter is found to be relatively strong and proiokes’a reduction by 2OF of the stretching frequency ~f0Hf and an increase by 200% of the out-of-plane deformation’T(OH) and by 2% of the in-
plane bending 6(OH). It provokesalso the appearance of the intermolecular stretching of001 at 194 cm’*_ the intermoiecutar
out-f-plane
twisting ~(00)
at 324 ~-II-~, and two in-plane 00
1. Introduction The expansion of low frequency spectroscopy in recent years has allowed the study of iotermoleculai vibrations
of the hydrogen
bond.
Nevertheless,
bending modes at 78 and 135 cm-*.
terferonieter RiIC coupled with a digital-analys& FTC f00-7-giving directly the intensity spectrkm versus the frequency from 20 to 400 cm-l.
one
notices that the chemical systems examined are rarely those of which intramolecular vibrations have been pteviousiy determined by studies in the near- and midinfrared regions. In addition to this, these works were frequently done with solid samples; and: a$ is we:1 known, in t&is physicalstate not only the hydrogen’ bond X-H...Y, but also chain mul~~ers can exist [l--S] i or a great number.of moleiules can be found in the same unit cell [6]. The dilute soiution of the. complex in an inert soIvent could present the advantage of offering an isolated hydrogen bond [7-g]. Hqwever; the rare works thai.have beeri done in the low frequency region were restricted solely to the stretching a(XY) [7,8]. 1. :,‘. We have examined, in the liquid,phase, a great. number df hydrogen bonded complexeS in quasi-inert. soltients, on +wide frequency-range, ffijrn 4000’tp 20,
2. Results
and discussion
Under the influence of the hydrogen bonding, the vibrations r&It&g from the phenolic and pyridinic rings are slightly
affected;
On the contrary,
those C.&r-
responding to the groups C-O-H of phenol and N-O of py~d~oxide are very strongly modified. We note effectively an important reduction, by 20%, of the stretching frequency b(OH), the spectral profile showing’many sub-maxima (fig. l), and’an incre,asirfg of the out-of-plane deformation r(OH) and of the in: plane bending S(OH) frequencies &pectively by. 20% and.256. The v(CO’j stretching frequency is also :j fdund to be incieased (table- I). We must mention ‘1’
that although these general spectial modifications
‘.’ z
have be& currently’exp&ted f9-12]., one’can &rely ? find them wiih the gne proton donor: As to the ,T[: v(QN), frequency itself,.a lo+ering qf about 50 cm-l .<. .; ;,.-. is-observed. ,‘;
~Ohme L3, number 2
CHEMICALPtiSICS
15.February
LETTERS
.1972,
The spectrum recorded in the low frequency Te&on shows, for the C6HSOH...0NC,H4CI$3 syst+n .. in dilute solution in carbon disulphide, three intense bands at 324,194 and 78 cm-l and a weak absorp--tion at 135 cm- 1 (fig. 2). The Grst band does,nct correspond’to the phenol bending -f(OH). This latter
has been identified in free phenol tit 315 [IO] and is shifted to 825 cm;1 inpresence of the o’rganic base. The’ identification is also confirmed by the deuterium-hydrogen substitution (table 1). The new bands are due, in consequence, to inter-. molecular vibratory modes. One of.the simplest methods of assignment of the
new absorptions consist of consideringrihe molecular complex as a polyatomic entity containing two point
Fig. 1. Infrared spectrum of phenol-methylpyridinoxide complex in CCL,. Concentration in phenol: 0.01 mole/l; concentration in pyridinoxide: 0.005 mole/i,cell thickness: 0.5 cm.
masses centered at the atoms C of phenol and-N of the organic base gnd to keep intact the other atoms,
involved directly in the hydrogen bond. This superC-OLH...O-N, of the maximum symmetry C, and composed with 5 atoms, has then nine vimolecule;
brations with 7 A’ (in-plane) and 2 A” (ok-of-plane): We can enumerate easily the five imiamolecular vibrations
(table
-41,: W;;,
0.01 mole/l, cell thickness:
Vibrational
(cm-‘)
0.2 cm.
Table
frequencies
WO),
1
of C-O-H and C-O-D groups of PhenolsCeHsOH and C,&OD pyridinoxide in dilute solution in CC& and in CS2
C6H50H Vibrations
with Cmethyl-
bonded
free
bonded
-2
cc14
(32
cc14
cs2
cc14
-2
3610
3593
307s
3060
2665
265.5
1341 311 1177
1340 314 1176
1385 c) 1244 c)
1380 825 1243
1025 ., 254 916
1024 2.55 919
2340 107.5 618 932
1074 617.. 929
1227
1226
dOHI ‘smj) rKW 7(CO)
a) Stretchiig
free and bonded
%%?D
free cc14
Ye)
@N);
The other four vibrations are intermolecular; they can be represented schematically in fig. 3. These oscillatory modes are to be compared with those existing in solid-methanol; the analysis of these latter modes is done very recently [3,4]. The com-
Fin. 2. Far-infrared spectrum of phenol-methylpyridinoxide complex in CS2. Concentration & phenol: 0.1 iolejl; concentration in pyridinoxide:
WH),
1):
:
.I260
1261 1245b)
no7b) .:
frequency o(ON) of methylpyridinoxide.
CC!~, these vibrations
appear respectively
:
‘_ . .
,1243 b)
12oyb)
b) In C!H3N07 ‘z solvent. c) With $e phenol-pyridine ,_ -. ‘. :,.. . :. ,, ,‘. ‘. ._.I ;. ._ ‘. ; ‘.” ...’ ./
._,’
-. complex
diluted p
:
at 1380 and at 1239 cm;*.
I ,.
:
:
::
. ‘.:. ,163’., ,‘.‘; ;_
Volu&i3,
number 2.
15 February 1972
CHEMICALPHYSICSLETTERS
.-
:
I?4 PLANE
-R
iO0)
(RI
)
(A')
IN PIANE RESDISC;
:)UT OF PIAXE DEFORMATION
Fig. 3. Intermolecular
(00)
TtiISTlNG
vibrarions (schematic) hydrogen bond.
of an isolated
A&nowIedgement
garison of the geometrical structure and the intermolecular vibrations of the two systems can help in the assignment of our spectrum. It is easy to identify the 00 sfrerch!ng, o(OO), to the absorption situated at 194 cm-l for the complex dissolved. in carbon disulphide. In a less active solv&it, like carbon tetrachloride [9], this vibration appears at 188 cm-l. This shift is coherent with the fact.that the OH stretching frequency, v(OH), is higher in the latter solvent than in carbon disulphide. This result confirms that for X-H.._Y hydrogen bonds, the stretching o(XY) frequency increases when the stretching v(XH) frequency decreases [ 1 I] . In our complex, tlie our-of-plane 00 defonnariurz, n(OO), that may be compared with the similar motion which appears at 348 cm- 1 in solid a-methanol [4], would be, with the minimllm doubt, the origin of the absorption situated at 324 cm-l. The last bands are due in consequence to the two in-plane-bending motions (COO) and,(OON) of the complex. One,must notice that in a hydrogen bonded system W-O-H...O-2
wheie
in pha& ancj of oppoiite phase. The latter mode can’ be assimilated to an 00 twisting, ~(00) and would app&r at a higher frequency than the former. Inthe &H50H...0NC5HqCH3 complex, the 00 bending which is the most similar to this latter motion is the OON bending; we call it the in-plane 00 twisting, T(OO).. It appears at 135 cm-l. The last absorption at 78 cm-l can then be assigned to the 00 bending mode, /3(00).
W = 2, because
the ex-
istence of a pseudo symmetry center, the two described motioqs must combine one with the other to give rise to two 00 bending m&ions in which the displacement of the two oxygen atoms is respectively
The authors are grateful to Professor J. Lascombe for helpful discussions.
References [I] R.J. Jakobscn and J.W. Brasch, Spectrochim. (1965)
Acta 21
1753.
[2] R.J. Jakobsen, J.W. Brasch and Y. Mikawa, Appl. Spectry. 22 (1968) 641. 131 A.B. Dempster and G. Zerbi, J. Chem. Phys. 54 (1971)
3600. [4] P.T.T. Wang and E. Whalley. J.Chem. Phys. SS (1971) 1830. [S] K. Ito and T. Shimanouchi, Biopolymers 5 (1967) 921. [6] R. Foglizzo and A. Novak, J. Chcm. Phys. 50 (1969) 5366. [7]
S.G.W.
Ginn and’J.i.
Wood,
Spectsochim.
Acta 23A
(1967) 621. [8)
G. Lichtfus and T. Zeegers-Huyskens,J. Mol. Struct. 9 (1971) 343.
[91 P.V. Huong and J.C. Lassegues, Spectrochim. Acta 26A (1970) 269.
[lo] P-V. Huong, M. Couzi and J. Lascombe, J. Chim. Phys. 64 (1967) 1056. [ 111 P.V. Huong and G. Turreli, J. Mol. Spectry. 25 (1968) 185.
[ 121 S. Yon-Bo and V.hi. Chulanovskii, 2 (1963) 218.
Opt. i Spektroskopiya,