Double bond stretching

A hypsochromic shift of 20-50 cm is observed in the double-bond stretching region, when the enamines are converted to the corresponding iminium salts by the electrophilic addition of a proton at the /3-carbon atom. The shift is accompanied by an enhancement in the intensity of the band. Leonard and co-workers (68,71-74) have used this absorption shift as a diagnostic tool for the determination of the position of the double bond... 

Double-Bond Stretching Frequencies of Enamines and Their Perchlorate Salts... 

The structure of the protonated enamines has been investigated by infrared spectroscopy. On protonation there is a characteristic shift of the band in the double-bond stretching region to higher frequencies by 20 to 50 cm with an increased intensity of absorption (6,13,14a). Protonated enamines also show absorption in the ultraviolet at 220-225 m/x due to the iminium structure (14b). This confirms structure 5 for these protonated enamines, because a compound having structure 4 would be expected to have only end absorption as the electrons on nitrogen would not be available for interaction with the n electrons of the double bond. 

No systematic IR spectroscopic studies have been reported. The value for the C-C double-bond stretching frequency of the enol ether structure in 2,7-dimethyloxepin is 1660cm-1.12... 

Only limited IR spectroscopic data for (benzo)thiepins have been reported. The C —C double bond stretching frequency in 2,7-di-rm-butyl-4,5-dimethylthiepin is observed at 1620 cm-1 with weak intensity.13 Characteristic strong intensities are found for the S —O vibrations in sulfoxide (e.g., 1040 cm-1 for 5-methoxy-4-phenyl-l-benzothiepin-3(2//)-one 1-oxide14) and sulfone (e.g., 1120 and 1300 cm-1 for thiepin 1,1-dioxide15) derivatives. 

Angell (1) has investigated the Raman spectra of acetonitrile, propylene, and acrolein on a number of zeolites and found that physical adsorption occurred. There are sufficient differences between the spectrum of the liquid and of the adsorbed species (e.g. the carbon-carbon double bond stretching in the case of propylene and the carbon-nitrogen triple bond stretching in the case of acetonitrile) to make it quite clear that it was not merely a case of condensation in the pores of the solid adsorbent. 

The band at 1600 cm-1 due to a double-bond stretch shows that chemisorbed ethylene is olefinic C—H stretching bands above 3000 cm-1 support this view. Interaction of an olefin with a surface with appreciable heat suggests 7r-bonding is involved. Powell and Sheppard (4-1) have noted that the spectrum of olefins in 7r-bonded transition metal complexes appears to involve fundamentals similar to those of the free olefin. Two striking differences occur. First, infrared forbidden bands for the free olefin become allowed for the lower symmetry complex second, the fundamentals of ethylene corresponding to v and v% shift much more than the other fundamentals. In Table III we compare the fundamentals observed for liquid ethylene (42) and a 7r-complex (43) to those observed for chemisorbed ethylene. Two points are clear from Table III. First, bands forbidden in the IR for gaseous ethylene are observed for chemisorbed ethyl-... 

The analysis of relations between intensities in the region of double bond stretching vibrations >c=n in the Raman spectra, allows one to arrive at a conclusion about s-cis- or s-trans -conformation of multiple bonds. The ratio between intensities of the high-frequency band to the low-frequency one for s-trans -conformers appears usually to be more than 0.5, whereas for s-cis -conformers it is less than 0.25 (393, 394). 

Both the calculated and observed spectrum are dominated by a very intense band (expt 2085 cm" and calcd 2439 cm" ) which has now been assigned to the ketene double-bond stretch. This particular absorption had been responsible for the earlier confusion over the triple-bond stretch in o-benzyne since the presence of even small amounts of 4a in reaction mixtures containing o-benzyne showed an absorption... 

H. Hamaguchi I would like to comment on the stilbene photoisomerization in solution. We recently found an interesting linear relationship between the dephasing time of the central double-bond stretch vibration of Si franj-stilbene, which was measured by time-resolved Raman spectroscopy, and the rate of isomerization in various solutions. Although the linear relationship has not been established in an extensive range of the isomerization rate, I can point out that the vibrational dephasing time measured by Raman spectroscopy is an important source of information on the solvent-induced vibrational dynamics relevant to the reaction dynamics in solution. 

The infrared spectra of the cycloproparenes are characterized by a weak band that appears between 1660 and 1690 cm"1 due to a combination of the aromatic double bond stretch with the three-membered ring skeletal vibration. Angular fused cyclo-propa[a]naphthalene (10) has the highest value (1687 cm"1) while for linear 11 it is more usual at 1673 cm"1, and cyclopropa[6]anthracene falls between these at 1678 cm"1. The... 

Exercise 9-12 Classify the following molecules according to the general characteristics expected for their infrared and Raman spectra (a) HC=CH (b) ICI (c) CO (d) CF2=CH2 (double-bond stretch only) (e) (CH3)2C—CH2 and CH3CH=CHCH3 (double-bond stretch only). 

In the infrared spectrum there is a marked shift (20-50 cm ) of the absorption maximum in the double-bond stretching region to higher... 

The VCD of helical, single and double stranded ribonucleic add (RNA) polymers was first reported by Keiderling s group in vibrations associated with double bond stretching vibrations of the bases in RNA [53]. The optical activity was found to be due to the coupling of the virtually achiral stretching vibrations which are arranged in a... 

The isomerization proceeds via an intermediate compound that is symmetrical at the C-8 position and that exhibits a continuous conjugated system of double bonds stretching from the enol double bond up to the indole system. Thus, isomerization of dihydrolysergic acids, in... 

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