Conformational response of tartaric acid to derivatization: Role of 1,3-dipole-dipole interactions

Abstract

The four-carbon chain in (R,R)-tartaric acid derivatives is predominantly antiperiplanar (trans) in the acid, its salts, esters, and NH-amides, while (-)-synclinal (gauche) conformer is the most abundant in N,N'-tetraalkyltartramides. Trialkylsilylation or tert-butylation of the hydroxy groups at C2 and C3 does not appear to affect the conformational preference of NH-tartramides, but it does change the conformational equilibrium in the case of tartrates (toward (-)-gauche) and N,N'-tetraalkyltartramides (toward trans), as judged from the NMR data. X-ray diffraction data point to the stabilizing role of antiparallel dipole-dipole interactions due to the 1,3-CO/CH bonds. These interactions can be found in the trans and (-)-gauche conformers but are not possible for the (+)-gauche conformers of (R,R)-tartaric acid derivatives. This rationalizes small proportion of (+)-gauche conformers in tartaric acid derivatives and points to a significance of 1,3-dipole-dipole interactions. The conformation around the C1-C2 (and C3-C4) bond is different in tartrates (O-C-C=O, syn) and tartramides (O-C-C=O, anti); the CD data (n-pi* band) show that O-silylation or O-tert-butylation brings about conformational changes around the C1-C2 bond in the case of N,N'-tetraalkyldiamides only.

From Single Molecule to Crystal: Mapping Out the Conformations of Tartaric Acids and Their Derivatives

“…Here a trans conformation introduces significant crowding of the substituents, whereas steric crowding due to dialkylamino substituents is absent in the case of conformers (+)-gauche, according to calculations. [20] The presence of such dipoles brings about an additional stabilizing effect, J and K, although apparently less significant than hydrogen bonding. Conformers (+)-gauche are the lowest-energy structures calculated for molecules in vacuo.…”

A circular dichroism – DFT method for conformational study of flexible molecules: the case of 1- and 2-naphthyl diesters

“…Therefore, the 1,3-dipole-dipole interactions determine the conformation around the γ, γ' angles. 32 The exception is the lowest energy conformer of 2a, where the overall molecular structure is affected by the formation of a set of intramolecular hydrogen bonds between carbonyl oxygen atoms and α-hydroxyl groups. For this structure the conformation around both γ and γ' angles is synclinal.…”

Probing the shapes of chiral bis-(o-naphthalimidobenzoyl) systems using X-ray and circular dichroism methods

“…3(a). We have already signaled the crucial role of 1,3-CH/CO dipole-dipole interactions in stabilizing the molecular conformation of tartaric acid derivatives and salts (Gawroń ski et al, 2005). Furthermore, the NAB units in the B conformation are involved in intramolecular C-H(aliphatic)Á Á Á(aromatic) interactions which together with 1,3-CH/ CO local dipole-dipole interactions might stabilize the overall conformation of molecules (2) and (3), i.e.…”