1H nuclear magnetic resonance and x-ray study of dihedral bond angles in the gauche O·CH2·CH2·O moiety of cyclic 7,8-dihydrodibenzo[f,h]-[1,4]dioxecin
article
The 1H n.m.r. spectra of the CH2·CH 2 groups in two ortho, ortho', ·CH2· X·CH2·CH2·X·CH 2· bridged biphenyl derivatives (I) (X = -O-) and (II) (X= MeN<) have been analysed. A set of four coupling constants has been derived: 3JAA', 3JBB', 3J AB' (= 3JA'B), and 2JAB. The 3JHH values were found to be only slightly temperature- and solvent-dependent. These coupling constants were used for a study of the geometry of the ·X·CH2·CH 2·X· moiety of these molecules in solution. Dihedral bond angles were calculated by use of various known 3J HH/φ relationships and the results compared with those obtained from an X-ray study of the ·O·CH2·CH 2·O bridged derivative (I). Crystals of (I) are orthorhombic, space group Aba2, with Z = 4 in a unit cell of dimensions a = 11.871 (1). b = 13.882(2), c = 7.875(2) Å. The structure was determined by direct methods and refined by least-squares techniques to R 0.033 for 410 observed reflections. The molecules have C2 symmetry. Dihedral bond angles between the coupled proton pairs are 31(4), 77(6), and 176(8)°. The 3J HH/φ relationship predicts successfully the deviation from the idealized value of 60° for the gauche-oriented proton pairs in (I).
TNO Identifier
228218
ISSN
1472779X
Source
Journal of the Chemical Society, Perkin Transactions 2(14), pp. 1942-1947.
Pages
1942-1947
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