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Vibrational spectra of 1-butanol
Journal of Molecular Structure, 42 (1977) 27-30 @Elsevier Scientific Publishing Company, Amsterdam
VIBRATIONAL
G. A. CROWDER Department (Received
SPECTRA
and MARY
of Chemistry,
-
Printed
in The Netherlands
OF l-BUTANOL
JANE
TOWNSEND
West Texas State Uniuersdy,
Canyon,
Texas
79016
(USA.)
4 May 1977)
ABSTRACT Infrared and Raman spectra were obtained for 1-butanol that showed the presence trans and gauche conformers in the liquid, vapor, and amorphous solid, but only the trans conformer is present in the annealed solid.
of
INTRODUCTION
Fukushima and Zwolinski [l] have made vibrational assignments for 1-propanol, and they list several references to the IR and Raman spectra of I-propanol. They concluded that the trans conformer [CA=+C-o ] is the principal form that exists in the liquid state, but they also concluded that a gauche conformer is also present. In later work, Abdurahmanova et al. [2] confirmed by microwave spectroscopy the presence of both tram and gauche conformers. Van der Maas and Lutz [3] have made a study of the OH stretch band of a large number of alcohols, some of which show two O-H bands that result from rotational isomers. The latter authors were unable to tell if 1-butanol exhibits rotational isomerism, but they concluded that the primary straight-chain alcohols they studied are always present in the same favorable conformation, or that the different conformations about the C-C axes have no effect on the O-H frequency. Vibrational spectra have not been published for 1-butanol, so IR and Raman spectra have been obtained for this compound in order to study the conformational behavior of this molecule. EXPERIMENTAL
Infrared spectra were obtained with a Beckman IR.12 spectrophotometer. Raman spectra were obtained with a Beckman model 700 spectrometer equipped with a Coherent Radiation Labs model 54 argon ion laser. The 488.0 nm line was used. The sample of n-C4H90H was obtained from Chemical Samples Company, and was redistilled before use.
28 RESULTS
AND
DISCUSSION
The liquid-state IR spectrum of 1-butanol isshown in Fig. 1 and the &man spectrum is shown in Fig. 2. The liquid is obviously 100% associated through hydrogen bonding, as the O-H stretch and C-OH torsion bands show. Solution spectra show the normal partial dissociation into the monomer. with the appearance of the monomeric O-H stretch band at -3640 cm-‘. However, the C-O-H bend of the monomer could not be detected in the solution spectra, either because of low intensity of this band and/or because of overlapping bands. The vapor-state IR spectrum was also obtained, and it shows the O-H stretch at -3675 cm-’ (Fig. 3). The C-O-H bend should shift to a iower wavenumber in the vapor (and solution) state, but no band that was absent for the liquid appeared in the proper region. Liquid and vapor-state bands are observed at -1218 cm-‘, which is probably due to both C-O-H bend (vapor only) and CH2 twist. The C-O-H bend in 1-propanol was observed at 1218 cm-’ in the vapor state [l]_
3500
3100
2
Fig. 1. Infrared spectrum
Fig. 2. Liquidstate
0
I 1500
of 1-butanol
Raman spectrum
I
I
I
1300
(neat).
of 1-butanol.
1
1100
I cm-1
900
I
I 700
I
I 500
T 2800
a
Fig. 3. Infrared spectrum of 1-butanol vapor.
Infrared spectra were also obtained for n-C,H,OH in the solid state by cooling a liquid film held between salt plates. The resulting spectrum was
essentially equivalent to that of the liquid, with the main differences being changes in relative intensities of some of the bands and a shift of the broad OH torsional band from a band centered at -660 cm-’ in the liquid to -690 cm-’ in the solid. However, when the solid was annealed for a short period of time, changes in the spectrum occurred, as the apparent result of crystallization of the solid. The two solid-state spectra are shown in Fig. 4. Figures 1 and 4 show that several bands that are present in the spectra of the liquid and amorphous solid are absent in the spectrum of the annealed solid. This disappearance of bands must result from the conversion of one or more rotational isomers into the one that is most stable in the crystalline lattice. The crystallization also resulted in another shift of the broad OH torsion, down to -620 cm-‘, and the appearance of a sharper band at -660 cm-‘. The C-C stretch band is expected to be conformation dependent, and should be observed in the 1000 cm-’ region, as was the case for 1-propanol. The spectra of the liquid and amorphous solid show five bands between 1000 and 1100 cm-‘, and these should consist of mixtures of C-C stretch, C-O stretch, and CHS rock. Three of these bands are absent in the spectrum of the crystals. Comparison of this spectrum with that of 1-propanol led to assignment of the band observed at 998 cm-l (in Fig. 4) to the C-O stretch. Preliminary normal coordinate calculations in this laboratory also indicate assignment of this band to the C-O stretch of the trans conformer (oxygen trans to the third carbon) and assignment of the 953 cm-’ band, which is absent in the spectrum of the crystals, to the gauche conformer. The C-O stretch of the trans conformer of 1-propanol was observed at 971 cm-‘, but the calculated value was 949 cm-’ and the calculated value for the gauche
conformer was 917 cm-’ [ 11. The present assignments are consistent with those results.
30
-
cm-1
900
cm-l 700
Fig. 4. Infrared spectra of 1-butanol. Lower curve, amorphous solid at -80 K; upper curve, annealed solid at -80 K. (The flat portion of the 620 cm-’ band results from 100% absorption of this band.) ACKNOWLEDGEMENTS
The authors are grateful to The Robert A. Welch Foundation, Houston, Texas and the Killgore Research Center for financial support of this work. REFERENCES 1 K. Fukusbima and B. J. Zwolinski, J. Mol. Spectrosc., 26 (1968) 368. 2 A. A. Ab’durahmanova, R. A. Rahimova and L. M. Ivanov, Phys. I&t. A, 32 (1970) 123. 3 J. H. van der Maas and E. T. G. Lutz, Spectrochim. Acta Part A, 30 (1974) 2005.
VIBRATIONAL
G. A. CROWDER Department (Received
SPECTRA
and MARY
of Chemistry,
-
Printed
in The Netherlands
OF l-BUTANOL
JANE
TOWNSEND
West Texas State Uniuersdy,
Canyon,
Texas
79016
(USA.)
4 May 1977)
ABSTRACT Infrared and Raman spectra were obtained for 1-butanol that showed the presence trans and gauche conformers in the liquid, vapor, and amorphous solid, but only the trans conformer is present in the annealed solid.
of
INTRODUCTION
Fukushima and Zwolinski [l] have made vibrational assignments for 1-propanol, and they list several references to the IR and Raman spectra of I-propanol. They concluded that the trans conformer [CA=+C-o ] is the principal form that exists in the liquid state, but they also concluded that a gauche conformer is also present. In later work, Abdurahmanova et al. [2] confirmed by microwave spectroscopy the presence of both tram and gauche conformers. Van der Maas and Lutz [3] have made a study of the OH stretch band of a large number of alcohols, some of which show two O-H bands that result from rotational isomers. The latter authors were unable to tell if 1-butanol exhibits rotational isomerism, but they concluded that the primary straight-chain alcohols they studied are always present in the same favorable conformation, or that the different conformations about the C-C axes have no effect on the O-H frequency. Vibrational spectra have not been published for 1-butanol, so IR and Raman spectra have been obtained for this compound in order to study the conformational behavior of this molecule. EXPERIMENTAL
Infrared spectra were obtained with a Beckman IR.12 spectrophotometer. Raman spectra were obtained with a Beckman model 700 spectrometer equipped with a Coherent Radiation Labs model 54 argon ion laser. The 488.0 nm line was used. The sample of n-C4H90H was obtained from Chemical Samples Company, and was redistilled before use.
28 RESULTS
AND
DISCUSSION
The liquid-state IR spectrum of 1-butanol isshown in Fig. 1 and the &man spectrum is shown in Fig. 2. The liquid is obviously 100% associated through hydrogen bonding, as the O-H stretch and C-OH torsion bands show. Solution spectra show the normal partial dissociation into the monomer. with the appearance of the monomeric O-H stretch band at -3640 cm-‘. However, the C-O-H bend of the monomer could not be detected in the solution spectra, either because of low intensity of this band and/or because of overlapping bands. The vapor-state IR spectrum was also obtained, and it shows the O-H stretch at -3675 cm-’ (Fig. 3). The C-O-H bend should shift to a iower wavenumber in the vapor (and solution) state, but no band that was absent for the liquid appeared in the proper region. Liquid and vapor-state bands are observed at -1218 cm-‘, which is probably due to both C-O-H bend (vapor only) and CH2 twist. The C-O-H bend in 1-propanol was observed at 1218 cm-’ in the vapor state [l]_
3500
3100
2
Fig. 1. Infrared spectrum
Fig. 2. Liquidstate
0
I 1500
of 1-butanol
Raman spectrum
I
I
I
1300
(neat).
of 1-butanol.
1
1100
I cm-1
900
I
I 700
I
I 500
T 2800
a
Fig. 3. Infrared spectrum of 1-butanol vapor.
Infrared spectra were also obtained for n-C,H,OH in the solid state by cooling a liquid film held between salt plates. The resulting spectrum was
essentially equivalent to that of the liquid, with the main differences being changes in relative intensities of some of the bands and a shift of the broad OH torsional band from a band centered at -660 cm-’ in the liquid to -690 cm-’ in the solid. However, when the solid was annealed for a short period of time, changes in the spectrum occurred, as the apparent result of crystallization of the solid. The two solid-state spectra are shown in Fig. 4. Figures 1 and 4 show that several bands that are present in the spectra of the liquid and amorphous solid are absent in the spectrum of the annealed solid. This disappearance of bands must result from the conversion of one or more rotational isomers into the one that is most stable in the crystalline lattice. The crystallization also resulted in another shift of the broad OH torsion, down to -620 cm-‘, and the appearance of a sharper band at -660 cm-‘. The C-C stretch band is expected to be conformation dependent, and should be observed in the 1000 cm-’ region, as was the case for 1-propanol. The spectra of the liquid and amorphous solid show five bands between 1000 and 1100 cm-‘, and these should consist of mixtures of C-C stretch, C-O stretch, and CHS rock. Three of these bands are absent in the spectrum of the crystals. Comparison of this spectrum with that of 1-propanol led to assignment of the band observed at 998 cm-l (in Fig. 4) to the C-O stretch. Preliminary normal coordinate calculations in this laboratory also indicate assignment of this band to the C-O stretch of the trans conformer (oxygen trans to the third carbon) and assignment of the 953 cm-’ band, which is absent in the spectrum of the crystals, to the gauche conformer. The C-O stretch of the trans conformer of 1-propanol was observed at 971 cm-‘, but the calculated value was 949 cm-’ and the calculated value for the gauche
conformer was 917 cm-’ [ 11. The present assignments are consistent with those results.
30
-
cm-1
900
cm-l 700
Fig. 4. Infrared spectra of 1-butanol. Lower curve, amorphous solid at -80 K; upper curve, annealed solid at -80 K. (The flat portion of the 620 cm-’ band results from 100% absorption of this band.) ACKNOWLEDGEMENTS
The authors are grateful to The Robert A. Welch Foundation, Houston, Texas and the Killgore Research Center for financial support of this work. REFERENCES 1 K. Fukusbima and B. J. Zwolinski, J. Mol. Spectrosc., 26 (1968) 368. 2 A. A. Ab’durahmanova, R. A. Rahimova and L. M. Ivanov, Phys. I&t. A, 32 (1970) 123. 3 J. H. van der Maas and E. T. G. Lutz, Spectrochim. Acta Part A, 30 (1974) 2005.