J. Edgar Anderson

The effect of exocyclic conjugation on the inversion of a saturated six-membered ring. A dynamic NMR study of N-substituted morpholines.

Abstract The effect of exocyclic conjugation on the inversion of a saturated six-membered ring is shown in a dynamic nmr study of a series of N-substituted morpholines where the substituents have similar shapes but different conjugating ability. As conjugation increases the ring inversion barrier decreases in contrast to previous observations of an unsaturated ring with conjugating substituents.

One-bond C–H NMR coupling constants in 1,2,4-trioxanes: a reversed perlin effect

In a reversal of the Perlin effect, the values of 1JC–H for the equatorial protons at C(3) and C(6) in 1,2,4-trioxanes are less than those for the corresponding axial protons; this is ascribed to homoanomeric interactions between equatorially directed nonbonding electron pairs on oxygen and the equatorial C(3)–H or C(6)–H σ* orbitals.

An NMR and ab initio MO study of the effect of β-oxygen in 1,3-dioxanes

NMR Measurements and ab initio calculations suggest that in 1,3-dioxanes the β-oxygen atoms have the effect of weakening the equatorial CH bond at the 5-position.

Conformational equilibria and barriers to rotation in monohalogenobutanes with methyl substituents. Methyl–halogen interactions. The size of a halogen atom

An n.m.r. study of barriers to rotation and conformational equilibria in 2-halogeno-2, 3, 3-trimethylbutanes and 2-halogeno-2, 3-dimethylbutanes is reported. Results are discussed in terms of the steric requirement of halogen atoms, and the interaction of these atoms with adjacent methyl groups.

The measurement of the one-fold rotational barrier of eclipsed bonds. A dynamic NMR determination of N–O or N–CH2 bond rotation in N-alkoxy- or N-alkyl-2,2,6,6-tetramethylpiperidines

In a series of N-alkoxy- and N-alkyl-2,2,6,6-tetramethylpiperidines, the temperature dependence of NMR spectra shows that a conformational interconversion involving ring inversion, nitrogen inversion and rotation about the exocyclic bond takes place. Barriers to interconversion are reported. Except with the simplest N-substituents, the rate-determining step in the interconversion is rotation about the exocyclic bond at nitrogen, so the measured barriers represent the one-fold rotational barriers for that bond.

Conformational studies by dynamic NMR. part 36.: The steric barrier and the π-barrier to rotation in simple enamines: diethylaminocyclohexenes

1-Diethylaminocyclohexene adopts a near-to-coplanar conformation at the N-Csp2bond with a 5.95 Kcalmol π-barrier to rotation through an orthogonal conformation with the lone pair in the π-p1ane. In contrast 1-diethy1aim no-2-methylcyclohexene adopts a non-planar conformation with the lone-pair near to the π-p1ane and a steric barrier to rotation of the diethylamino group through the plane, of 8.1 Kcalmol.

Setting the anomeric effect against steric effects in simple acyclic acetals. Non-anomeric non-classical conformations. An N.M.R. and molecular mechanics investigation

N.m.r. parameters for a series of simple aliphatic acetals indicate that the preferred conformation changes from the anomeric one found in formaldehyde dimethyl acetal (formal), to a new one whose structure is suggested by molecular mechanics calculations.

Chair–chair interconversion in some highly substituted 1,2,4-trioxanes and 1,3-dioxanes. A dynamic NMR study of a striking effect of skeletal substitution

A dynamic NMR determination of barriers to chair–chair interconversion in some tetra- and hexa-substituted 1,2,4-trioxanes and 1,3-dioxanes is reported. Two comparisons of trioxanes and equivalently substituted dioxanes show that trioxane barriers are strikingly higher, and this is attributed to the high barrier to rotation about the oxygen–oxygen bond in the trioxane series.

Eclipsed exocyclic carbon-oxygen bonds in the hexamethyl ether of scyllo-inositol. X-ray crystallographic and NMR studies

Abstract Hexa- O -methyl- scyllo -inositol was synthesized and its crystal structure was determined by X-ray diffraction. As predicted by calculations, each oxygen-methyl bond eclipses the adjacent carbon-hydrogen bond. NMR studies show that the same conformation predominates in solution.

Restricted C–C bond rotation in a solid measured by solid state NMR spectroscopy

1,1-Dibenzyl-2,2-dimethylpropan-1-ol 1 shows a coalescence phenomenon in its 13C solid state CP MAS NMR spectrum consistent with slowing of rotation of the tert-butyl group about the C(1)–C(2) bond with an activation energy of 13.1 kcal mol–1(1 cal = 4.184 J), 4 kcal mol–1 higher than in solution.