2.22 – Pyrans and Fused Pyrans: (i) Structure

Stereochemical splitting in NQR: Chloral hydrate

In a series of compounds with fragments OCsp3-Cl or OCsp2-Cl, O=CCl, the relationships observed in the changes in35Cl NQR frequencies are explained by geometric and energy characteristics of the orbitals n(0) andσ*(CCl).

35Cl NQR of cyclic α-chlorovinyl ethers and orbital interactions in O-C-Cl triad

1.

In dichloromethyl aryl ethers the n,π and n,σ interactions with the participation of the lone pairs of the O atoms are weakened in comparison to unsaturated ethers and the previously studiedα-chloro ethers.




2.

In solutions and liquid samples of dichloromethyl aryl ethers gauche, gauche and gauche, trans conformers with respect to the

bond coexist, and in crystals only gauche, trans conformers are realized.

Electronic and spatial structure of dichloromethyl aryl ethers

A 35Cl nuclear quadrupole resonance study of 2,2,3,3-tetrachlorotetrahydropyran (I) at 77 K has revealed an anomeric shift of ca. 2·4 MHz between the chlorine atoms in the 2-position; in 2,3,3-trichlorotetrahydropyran (II), similar arguments show that the 2-chlorine takes up an axial position in the solid state.

John A. S. Smith

Papers

Conformational studies of chlorotetrahydropyrans by nuclear quadrupole resonance spectroscopy