Infrared studies of some N-methylacetamide complexes

1970 ◽  
Vol 48 (13) ◽  
pp. 2090-2095 ◽  
Author(s):  
Y. H. Shaw ◽  
N. C. Li
Keyword(s):  
Hydrogen Bonding ◽  
Near Infrared ◽  
Mixed Solvent ◽  
Molar Absorptivity ◽  
Association Constants ◽  
Magnetic Resonance Frequency ◽  
Infrared Studies ◽  
Stretching Vibration ◽  
Infrared Method ◽  
Peptide Amide

Hydrogen bonding of N-methylacetamide (NMA) with dimethylsulfoxide (DMSO) and N,N-dimethylacetamide (DMA) in carbon tetrachloride and CCl4/CHCl3 mixed solvent was studied by a near-infrared method, which consists of measuring the effects of various concentrations of DMSO or DMA on the molar absorptivity of 0.06 M NMA at 6800 cm−1, corresponding to the first overtone of the uncomplexed NH stretching vibration. The association constants for the formation of 1:1 NMA–DMA and NMA–DMSO complexes in CCl4 are 10 and 121/mole, respectively, at 25°. In order to obtain an association constant for the formation of NMA–DMSO in CCl4/CHCl3 mixed solvent, it is necessary to have data on association constants of CHCl3–DMSO complexes in CCl4, and we have obtained these by determining the effects of various concentrations of DMSO on the proton magnetic resonance frequency of 0.05 M CHCl3 in CCl4. The association constants for the formation of NMA–DMSO and NMA–DMA in CCl4/CHCl3 mixed solvent are slightly higher than in CCl4, presumably due to hydrogen bonding between Cl3CH and C=O in NMA. NMA was chosen as the simplest molecule containing the peptide amide group and hence can be regarded as a structural unit of the polypeptide chain. Our results show that DMSO and DMA are effective in disrupting the interamide bonds, by acting as hydrogen acceptors to the NH group.

Hydrogen bonding in the vapour phase: an unusual type of infrared band

1970 ◽  
Vol 316 (1526) ◽  
pp. 303-313 ◽  
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Chloride ◽  
Near Infrared ◽  
Low Frequency ◽  
Vapour Phase ◽  
Infrared Band ◽  
Deuterium Chloride ◽  
Near Infrared Spectra ◽  
Bending Mode ◽  
Stretching Vibration

Association bands, due to vibrations of the hydrogen halides modified by hydrogen bonding, have been measured in the near infrared spectra of mixtures of alkyl cyanides with hydrogen chloride or deuterium chloride in the vapour phase. The vibration frequencies of the hydrogen bonds have been estimated. The association band found with mixtures of methyl cyanide and hydrogen chloride, or deutero derivatives of each of these molecules, shows a broad contour upon which a number of sharp peaks are superposed at the lower frequency side. These peaks have been interpreted as being due to an agglomeration of P lines near the band head in each of a series of hot bands which accompany the association band, and which arise from transitions from higher levels of a bending mode of low frequency. The latter appears to have a frequency in the range 20 to 60 cm -1 . The spectral analysis suggests that the excitation of the hydrogen halide stretching vibration leads to a shortening of the hydrogen bond.

Infrared studies on rotational isomerism. III. 2-Chloro- and 2-bromo-ethanol

1969 ◽  
Vol 47 (6) ◽  
pp. 901-910 ◽  
Author(s):  
Paul Buckley ◽  
Paul A. Giguère ◽  
Michel Schneider
Keyword(s):  
Hydrogen Bonding ◽  
Intramolecular Hydrogen Bonding ◽  
Rotational Isomerism ◽  
Apparent Discrepancy ◽  
Trans Isomers ◽  
Kcal Mole ◽  
Infrared Studies ◽  
Isotopic Molecule ◽  
Intramolecular Hydrogen ◽  
Unambiguous Assignment

The relative intensities of the C—X stretching bands of the gauche and trans isomers in the vapor were measured as a function of temperature up to 165 °C for 2-chloroethanol, and up to 130 °C for 2-bromoethanol. From these the enthalpy differences between the two isomers were found to be 1.20 and 1.45 ± 0.1 kcal mole−1 respectively for the two halogenated ethanols. Similar measurements on the O—H stretching bands gave values higher than the above by 0.45 kcal mole−1 for both compounds. This apparent discrepancy is interpreted as due to a second gauche isomer, the OH group of which is not engaged in intramolecular hydrogen bonding, and which is less stable than the trans isomer.A study of the isotopic molecule ClCH2—CH2OD has led to unambiguous assignment of the OH bending and torsional frequencies. The spectra of the solid show that 2-chloroethanol can exist in two different crystalline phases: a stable one consisting of gauche molecules only, and a metastable one containing both isomers.

Near-Infrared Method for Analysis of Block and Random Ethylene-Propylene Copolymers.

1966 ◽  
Vol 38 (2) ◽  
pp. 217-220 ◽  
Author(s):  
R. M. Bly ◽  
P. E. Kiener ◽  
B. A. Fries
Keyword(s):  
Near Infrared ◽  
Ethylene Propylene ◽  
Infrared Method
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