Low‐frequency Raman spectra of odd α,ω‐disubstituted n‐alkanes

Abstract

Low‐Frequency Raman spectra of odd α,ω‐dibromo‐ and α,ω‐dihydroxy‐n‐alkanes were recorded. The longitudinal acoustic mode (LAM‐1) frequencies were assigned by references to the published results for n‐alkanes and even α,ω‐disubstituted n‐alkanes and also by taking account of the effects of end intermolecular forces and end‐group masses by use of the chain model of Minoni and Zerbi.

Low-Frequency Raman Spectroscopy of n-Alcohols. LAM Vibration and Crystal Structure

“…Within a degree of approximation, the frequencies of LAM-1 bands can be calculated by using the model of an isolated elastic rod with free ends . The perturbation of the LAM-1 frequencies by end effects, such as interlayer forces and the inertial masses of end groups, has been investigated theoretically by modeling with a perturbed elastic rod , or a linear crystal, while extra insight has been gained by calculation of normal modes. ,, Experimental studies of these effects based on end-modified n -alkanes have been reported by several authors. − Reports from our laboratories have encompassed not only high-modulus trans-planar n -alkanes and their derivatives 17-19 but also low-modulus helical oligo(oxyethylene)s. − We have shown that the LAM-1 frequencies of trans-planar alkyl chains are very sensitive to end-group mass and relatively insensitive to temperature, while the LAM-1 frequencies of helical oligo(oxyethylene) chains are most sensitive to interlayer force and are more temperature dependent.…”

“…The low-frequency Raman spectra of several n -alcohols, with chain lengths between C 13 and C 30 , were recorded in the present study. Low-frequency modes were assigned on the basis of the spectra of the n -alkanes and their mono- and disubstituted derivatives, ,− and on calculation of frequencies via linear crystal and ab initio procedures. The probability that crystal structure plays a role in determining the LAM-1 frequency was considered, and with this in mind, the crystal structures of the C 17 and C 20 alcohols were determined.…”

The LAM-1 band in the low-frequency Raman spectra of even and odd monosubstituted n-alkanes

“…2 The perturbation of the LAM-1 frequencies by end e †ects, such as interlayer forces and the inertial masses of end groups, has been investigated theoretically by use of perturbed elastic rod models7,8 and crystal chain models.9 Experimental studies of these e †ects based on end-modiÐed n-alkanes have been reported by several authors.9h15 Previous reports from our laboratories have concerned a,x-disubstituted n-alkanes, and have covered a wide range of end groups. 14,15 In this paper we report the low-frequency Raman spectra of several even and odd monosubstituted n-alkanes at several temperatures in the range 173È300 K. Two aspects were considered : (i) the e †ect of chain length in the series of monobromoalkanes where n lies in the range 7…”

Determination of Percent Crystallinity of Side-Chain Crystallized Alkylated-Dextran Derivatives with Raman Spectroscopy and Multivariate Curve Resolution

“…LA mode is sensitive to a single carbon atom difference in the crystal lattice. The nature of end group such as the presence of heavy atom, hydrogen bonding, dimerization, etc., however, affects the frequency of LAM in the case of alkanes. − In the case of polymers (e.g., PE), the contribution from amorphous segments lying close to crystal lamella toward the LAM frequency has been investigated and there is a general agreement that contribution is mainly from lamellar core. , …”

“…62−64 In the case of polymers (e.g., PE), the contribution from amorphous segments lying close to crystal lamella toward the LAM frequency has been investigated and there is a general agreement that contribution is mainly from lamellar core. 65,66 Multivariate Curve Resolution by Alternating Least-Squares. Multivariate curve resolution (MCR)-alternating least-squares (ALS) 43−49 is a well demonstrated and effective multivariate statistical method for identifying hidden components whose linear combinations constitutes the original data matrix.…”