Krystyna Gawronska

Factors Affecting Conformation of (R,R)-Tartaric Acid Ester, Amide and Nitrile Derivatives. X-Ray Diffraction, Circular Dichroism, Nuclear Magnetic Resonance and Ab Initio Studies

Abstract Derivatives 2a–15a of (R,R)-tartaric acid (1a) with all combinations of methyl ester, amide, N-methylamide and N,N-dimethylamide groups, as well as the corresponding O,O′-dibenzoyl derivatives 1b–15b and nitriles 16–18 have been synthesized. Their conformations have been studied by the NMR and CD methods in solution as well as by X-ray diffraction in the crystalline state. The preference for planar. T conformation of the four carbon chain is observed under conditions restricting the α-hydroxyacid, ester or amide group to be nearly planar, this conformation being stabilized by intramolecular hydrogen bonds of the S(5) motif and the electrostatic CO/C(β)H and CN/C(β)H coplanar bond interactions. The C=O/C(α)-O bond system tends to be either synplanar (ester, acid), or antiplanar (ester, primary and secondary amide). Ab initio calculations allowed to demonstrate that for the isolated molecules of diamides 10a and 15a there is strong preference for gauche G+(a,a) conformers, the driving force being the formation of the hydrogen bonded six-membered cycles of the S(6) motif joining the OH and C=O groups from two different halves of the molecule. The results compare favourably with the experimental values derived from NMR spectra of 15a in nonpolar solvent. In the absence of intramolecular hydrogen bonding the N,N-dimethylamide group is better accomodated in a gauche G− conformer. This releases the nonbonded interaction due to the amide methyl group anti to the carbonyl group.

Conformational disparity of (R,R)-tartaric acid esters and amides

Abstract Exciton chirality method is used to determine anti and gauche conformations, respectively, of ester and dialkylamide derivatives of (R,R) - tartaric acid. Gauche conformation of (R,R)-N,N,N′-tetramethyltartamide and its O,O-dibenzoyl derivative is found in the solid state by X-ray analysis.

Novel chiral pyromellitdiimide (1,2,4,5-benzenetetracarboxydiimide) dimers and trimers: Exploring their structure, electronic transitions, and exciton coupling

The chiral but highly symmetrical acyclic and cyclic pyromellitic diimide dimers and trimers 2-5 have been obtained and characterized for the first time. The pyromellitdiimide chromophores in these molecules are linked by a rigid diequatorially 1,2-disubstituted cyclohexane skeleton. The structures of the compounds have been determined in detail by molecular modeling and, in the case of cyclic dimer 4 and trimer 5, by means of X-ray diffraction analysis. The electronically excited states of the pyromellitdiimide chromophore (1a) have been studied in these and other model compounds by means of linear dichroism (LD), magnetic circular dichroism (MCD), and circular dichroism (CD) spectroscopy. CD spectra of the rigid cyclic trimer 5 have provided the most detailed information on the excited states of the pyromellitdiimide chromophore. The low-energy tail (340-360 nm) of the absorption envelope can be assigned to out-of-plane polarized n-pi* transitions (I, II). The higher energy bands are due to contributions from up to six pi-pi* transitions, these being polarized either along the long (IV-VI, VIII) or short axis (III, VII). The results of ab initio CIS/cc-pVDZ and semiempirical INDO/S-CI calculations have been compared with the experimental data. CD Cotton effects in the region 200-260 nm, which result from exciton interactions between electric dipole allowed transitions of two pyromellitdiimide chromophores in compounds 2-5, provide reliable and useful information concerning the conformation and absolute configuration of these molecules, which may be extrapolated to other oligoimide systems.

Exciton coupling of the phthalimide chromophore: Application to configurational assignments

Abstract The absolute configuration of chiral β-phenyl substituted primary amines is readily correlated with the exciton Cotton effects resulting from the intramolecular interaction of the electric transition moments of the phthalimide derivative (220 nm π-π* band) with the benzene chromophore ( 1 L g band), compounds 1–3 . Similar correlation is applied to the exciton coupling between the π-π* band transition moments of the phthalimide and the benzoate chromophores derived from chiral vicinal amino alcohols, compounds 8–13

4,5-DIMETHOXYPHTHALIMIDE AND 6,7-DIMETHOXY-2,3-NAPHTHALIMIDE - TWO NEW CHROMOPHORIC DERIVATIVES FOR THE AMINO GROUP

We have developed new chromophoric derivatives for the amino group: 4,5-dimethoxyphthalimide and 6,7-dimethoxy-2,3-naphthalimide, particularly suitable for CD applications. These highly fluorescent imides show very strong Cotton effects due to exciton coupling which are red-shifted with respect to the parent phthalimide and 2,3-naphthalimide chromophores. No significant Cotton effects other than those due to the transition with the electric dipole transition moment colinear with the C2-axis of the chromophore were observed.

Synthesis and conformations of 2,3:4,5- and 2,4:3,5-di-O-isopropylidene-D-mannitol

Abstract The 2,3:4,5- ( 8 ) and 2,4:3,5-di- O -isopropylidene ( 10 ) derivatives of d -mannitol have been prepared from 1,6-di- O -benzoyl- d -mannitol and their structures established by 13 C-n.m.r. spectroscopy. The 1,3-dioxane rings in 10 adopt a skew conformation and the sugar carbon chain in 8 is bent around the C-3-C-4 bond, as found by i.r. data and molecular mechanics calculations. Oxidation of 8 with pyridinium dichromate gave 2,3:4,5-di- O -isopropylidene- d -mannono-1,6-lactone ( 12 ).

Exciton coupling in various substituted aryl-phthalimide bichromophoric systems☆

Abstract As demonstrated in this paper, exciton Cotton effects reflecting the absolute stereochemistry of the molecule can result from coupling between the allowed transitions of phthalimide. 3,6-dichlorophthalimide, 4,5-dichlorophthalimide or 3,4,5,6-tetrachlorophthalimide and p-substituted benzene, naphthalene, benzoate or cinnamate chromophores. This significantly extends the scope of application of phthalimide chromophoric derivatives to stereochemical assignments by CD spectroscopy. The direction of the transition moments in chlorinated phthalimide chromophores are determined from linear dichroism measurements of N -butyl derivatives oriented in polyethylene film.

Intramolecular Interactions of Trityl Groups

Trityl group, Tr, is a molecular dynamic rotor of which the conformation and helicity depend on other groups in the close vicinity. Interactions with another covalently linked Tr group and with other substituents are analyzed in terms of transfer of chirality to the trityl group. Two trityl groups in a molecule can mutually interact at a distance of two, three, or five bonds. Despite its size, a Tr group attached to a cyclohexane or cyclopentane ring through an oxygen or nitrogen atom adopts either an axial or equatorial position, depending on additional stabilizing interactions, such as hydrogen bonding.

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

Stereoisomers of one of the most important organic compounds, tartaric acid, optically active and meso as well as the ester or amide derivatives, can show diverse structures related to the rotation around the three carbon-carbon bonds. This study determines the controlling factors for conformational changes of these molecules in vacuo, in solution, and in the crystalline state using DFT calculations, spectroscopic measurements, and X-ray diffraction. All structural variations can be logically accounted for by the possibility of formation and breaking of hydrogen bonds between the hydroxy or amide donors and oxygen acceptors, among these the hydrogen bonds that close five-membered rings being the most stable. These findings are useful in designing molecular and crystal structures of highly polar, polyfunctional, chiral compounds.

Diastereoselective formation of chiral 2,2'-spirobibenz[d]chromene derivatives. Evidence from circular dichroism and crystallographic data

Condensation of optically active ketones, (3R)-methylcyclohexanone and 5α-cholestan-3-one, with 2-hydroxy-1-naphthaldehyde brings about formation of chiral 2, 2′-spirobibenz[d]chromene derivatives with diosteroelectivity 75% and 100%, respectively. Absolute configuration of the newly formed chiral center was determined through the application of the exciton chirality method and for the 2, 2′-spirobibenz[d]chromene derivative of (3R)-3-methylcyclohexanone confirmed by the X-ray crystallographic study.