G.A. Crowder

Vibrational analysis of 1-iodopropane, 1-iodobutane and 1,3-diiodopropane

Abstract Normal coordinate calculations were made for the trans and gauche conformations of n-propyl and n-butyl iodides and for the tt, tg and gg conformations of 1,3-diiodopropane. Nineteen force constants of a 48-parameter modified valence force field were adjusted to provide the best fit for 114 frequencies (excluding C-H) of all these conformations except for gg, 1,3-di-iodopropane. The average difference between observed and calculated wavenumbers was 6.6 cm−. Previous vibrational assignments were revised.

Vibrational analysis of ethyl and n-propyl fluorides

Abstract Infrared spectra of n-propyl fluoride in the gas and solid states were obtained that confirm the presence of two molecular conformations in the gas and unannealed solid. Only one conformation identified as the gauche form is present in the annealed solid. Raman spectra were obtained for the solid. Normal coordinate calculations were made simultaneously for ethyl fluoride, gauche n-propyl fluoride, and trans n-propyl fluoride, and the resulting force constants and vibrational assignments are given.

Rotational Isomerism in Bromoacetone and Fluoroacetone

Infrared spectra in the region 60–4000 cm−1 were obtained for bromoacetone and fluoroacetone for the vapor and liquid (or solution) states and for the solid state in the region 600–4000 cm−1. Spectra in the region 300–4000 cm−1 were obtained for solutions in carbon tetrachloride and acetonitrile. The spectra show that both these compounds exist as mixtures of rotational isomers, and that the less polar form is present in much higher amount in the vapor state than the more polar form. For bromoacetone, the more polar form is more stable in the liquid state, and is the only form present in the solid. For fluoroacetone, the two forms have about the same energy in the liquid, and both forms are present in the solid.

Rotational Isomerism in meta‐Halobenzaldehydes

Infrared spectra have been obtained for m‐chlorobenzaldehyde, m‐bromobenzaldehyde, and m‐iodobenzaldehyde. Each of these compounds exists as a mixture of two rotational isomers in the neat liquid. The cis‐O form of m‐chloro‐ and m‐bromobenzaldehyde is the low‐energy form, and is the only form present in the solid state. The trans‐O form of m‐iodobenzaldehyde is the only form present in the solid state of that compound, but the difference in energy between rotamers in the neat liquid is small. The stability of the cis‐O form of m‐bromo‐ and m‐chlorobenzaldehyde relative to the trans‐O form is attributed to the inductive effect of the halogen.

Infrared spectra and vibrational analysis of ethyl lodide and some deuterated derivatives

Abstract Infrared spectra were obtained for CH3CH2I, CH3CD2I, CD3CH2I, and CD3CD2I, and normal coordinate calculations were made with a 28-parameter valence force field that fit the 69 assigned frequencies with an average deviation of 5.4 cm−1. A quantitative description of the normal modes is given.

Vibrational analysis of n-butyl, n-pentyl, and n-hexyl fluorides

Abstract Infrared spectra were obtained for n -butyl, n -pentyl, and n -hexyl fluorides in the liquid and solid states, and liquid-state Raman spectra were obtained for the first two of these. Normal coordinate calculations were carried out and twenty force constants of the C-CH 2 F group were refined to provide the best fit for the 114 assigned frequencies of trans-n -propyl, gauche-n -propyl, TT-n -butyl, and TG-n -butyl fluorides. The resulting force constants were used to calculate the frequencies of the GT - and GG conformations of n -butyl fluoride and the two conformations for each of n -pentyl and n -hexyl fluoride that have coplanar carbon chains. The presence of all four conformers of n -butyl fluoride in the liquid state is indicated, but only the TG -conformer is present in the solid. The existence of the two conformations of n -pentyl and n -hexyl fluorides for which calculations were made is supported by comparison of the observed and calculated frequencies. Additional conformations seem to be present. The simplest solid-state spectrum is due only to the conformer that has a coplanar chain of carbons and the fluorine atom in the gauche position. Previous tentative conclusions about the relation between C-F stretching frequency and configuration have been revised.

Vibrational analysis of some dimethylhexanes

Abstract Infrared and Raman spectra were obtained for 2,2-dimethylhexane, 2,3-dimethyl-hexane, 2,4-dimethylhexane, and 2,5-dimethylhexane, and were interpreted with the aid of normal coordinate calculations. 2,2-DMH exists as two conformers, one with C s symmetry and the other with C 1 symmetry. The C 1 conformer disappears on solidification. Three conformers of 2,3-DMH were found experimentally, but a fourth one probably exists. The solid could not be crystallized. 2,4-DMH exists as three conformers, but the solid for this compound also could not be crystallized. 2,5-DMH exists as C i and C 2 conformers, but only the C i conformer is present in the crystalline solid. Calculations for the eleven molecules with transferred force constant values resulted in an average difference between observed and calculated wavenumbers of 4.4 cm −1 , or 0.37%, for 430 frequencies below 1500 cm −1 .

Vibrational analysis of 1-butyne and 1-pentyne

Abstract Infrared and Raman spectra have been obtained for 1-pentyne and normal coordinate calculations are made for 1-butyne and 1-pentyne. Comparison of the observed and calculated frequencies of 1-pentyne shows the presence of two conformations. The energy difference between conformers is approximately zero. Vibrational assignments are made for the three molecules.

Rotational Isomerism in Haloacetones. II. Iodoacetone

Infrared spectra for the vapor, liquid, and solid states of iodoacetone, and for solutions of iodoacetone were obtained. There are two rotational isomers present in approximately equal concentrations in the liquid state, but the less polar form is present in excess in the vapor. The more polar form is present in excess in the solid. Assignment of some of the fundamentals was made.

Vibrational analysis of some trimethylalkanes

Abstract Liquid and solid-state infrared spectra were obtained for 2,2,3-trimethylbutane, 2,2,3-trimethylpentane, 2,2,4-trimethylpentane and 2,3,3-trimethylpentane, and were interpreted with the aid of normal coordinate calculations. Trimethylbutane, 2,2,3-trimethylpentane and 2,2,4-trimethylpentane each exist as only one conformer, but either two or three conformers of 2,3,3-trimethylpentane are present in the liquid state. Only one conformer is present in the crystalline solid, and it was identified as one with only four of the five chain carbons coplanar. The average error for 246 calculated frequencies assigned to observed values for the six molecules is 5.2 cm −1 , or 0.59%