Rocking, methylene

The band resulting from the methylene rocking vibration (p CH2), in which all of the methylene groups rock in phase, appears near 720 cm-1 for straight-chain alkanes of seven or more carbon atoms. This band may appear as a doublet in the spectra of solid samples. In the lower members of the w-alkane series, the band appears at somewhat higher frequencies. 

Bauld, N. L. Cessac, J. Holloway, R. L. l,3(Nonbonded) carbon/carbon interactions. The common cause of ring strain, puckering, and inward methylene rocking in cyclobutane and of vertical nonclassical stabilization, p)U amidalization, puckering, and outward methylene rocking in the cyclobutyl cation, J. Am. Chem. Soc. 1977,99, 8140-8144. 

If all six methylenes rock, the chair is converted to another chair in which all six former equatorial hydrogens have become axial and the six axial hydrogens have become equatorial If only three methylenes rock, the cyclohexane ring will be in the boat conformation. It would then have four pairs of eclipsed hydrogens in addition to a stern-bow interaction. 

The FT-IR-ATR absorption spectrum of the control polypropylene (untreated) is shown in Figure 1. It is a typical polypropylene spectrum with absorption bands due to asymmetric and symmetric stretching of CH3 and CH2 groups around 2900 cm-1. The absorption bands at 1460 nd at 1380 cm-1 represent the asymmetric and symmetric bending of CH3 respectively. Absorption bands at 2878 cm-- - (CH3 stretching) and at 841 cm-- (Methylene rocking modes) suggest that the polypropylene membrane is of the isotactic form. 

Simonazzi (67) developed a procedure based on the integrated area of the methylene rocking band between 13 and 14 p (instead of this area, the sum of absorbances at 13.3, 13.64 and 13.85 p may be used). The IR spectrum is scanned between 12.5 and 15 p, keeping the sample at 120° C. For the Perkin-Elmer 221 spectrophotometer used for this analysis, the calibration line has the equation ... 

In hydrogen exchange reactions, the isotope effect apparently increases for substitution at the more reactive positions, whereas in most other electrophilic substitution reactions the isotope effect decreases. This reversal has been ascribed to the importance of a methylene rocking vibration in the transition state of... 

Ring-methylene rocking vibration (if not adjacent to the ring- oxygen atom) 867 d... 

Since the hexacyanometalate complexes can be of variable composition, it is important to have some means of determining whether a complex will have sufficient activity in an epoxide polymerization. This is possible by examining the infrared absorption spectra (2) of Nujol mulls of these complexes. For liquid 1,2-dimethoxyethane (glyme), the strong absorption at 851 cm has been assigned (ID)to the methylenic rocking mode. 

Snyder, R.G. Vibrational spectra of crystalline n- aralHns. I I. Methylene rocking and wagging modra. J. MoL Spectry. 4, 411—434 (1960) ... 

C. The next most prominent band in the IR occnrs near 720 cm . This absorption, which is assigned to the aU-in-phase methylene rocking vibration, has Utde or no intensity in the Raman effect. In the IR this band has been identified in those systems possessing fonr or more methylene gronps in a row (in systems with fewer than fonr methylene... 

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