Structural properties of methoxy derivatives of benzyl bromide, determined from powder X-ray diffraction data

Abstract

Structure determination of 3,5-dimethoxybenzyl bromide and 3,4,5-trimethoxybenzyl bromide has been carried out from laboratory powder X-ray diffraction data using the direct-space Genetic Algorithm technique for structure solution followed by Rietveld refinement. These two compounds are of interest for their potential use as building blocks for the synthesis of dendritic materials. Although the two molecules differ only in the presence/absence of the methoxy group at the 4-position of the aromatic ring, the structural properties of the two materials are significantly different. © 2005 International Centre for Diffraction Data.

2,6-Dimethoxybenzyl Bromide

“…As compared to the unsubstituted benzyl bromide 9 compound 1 shows lengthening of both ring-CH 2 and CH 2 -Br bonds and a torsion angle much closer to 90 • . In considering the data for the isomeric 3,5-dimethoxy compound 7, it should be noted that the first set of data [16] is derived from a powder diffraction study, and the discrepancy between this and the single-crystal data [17], as well as all the other values in Table 1, is likely to be due to systematic errors linked to the different technique. The situation for the apparently good model compound 10 is complicated by the fact that there are two separate crystal forms containing, respectively, three and two independent molecules in the unit cell and each molecule has all three CH 2 Br groups non-equivalent, thus delivering a total of 15 values for each parameter, which actually span the full range of values exhibited by the other compounds in the Table . Nonetheless, it can be seen that the parameters listed for 1 are broadly in line with those of closely similar compounds.…”

“…The 2,5-isomer 6 was first reported in 1953 [13] and full spectra were subsequently described [14]. The 3,5-isomer 7 was first prepared in 1962 [15] and is the only one of the six isomers to be characterised by X-ray diffraction to date, with both powder [16] and single crystal [17] data available. Interestingly, the 2,4-isomer 8 has a similar lack of characterisation to 1, being mentioned in two patents [18,19] as being generated from the corresponding alcohol and PBr 3 and used immediately without isolation, and in terms of data, only the 1 H-NMR chemical shift for its CH 2 is available [20].…”