Comments on the Crystal Structure of Polypivalolactone and Deviation of Ester Groups from trans Planarity

Abstract

(1974).The crystalline conformation of polypivalolactone was determined by analysis of the chain conformational energies and it was found that the minimum energy corresponds to a planar tmrzs conformation for the ester group. The result was con~pared to published X-ray data based on fiber diffraction which show a significant deviation from trans planarity. This difference is discussed in terms of the relative energies involved and by comparison with literature crystallographic results of low molecular weight carboxylic esters. It is stressed that because of the paucity of information in fiber diffraction, internal energy considerations are important for assigning internal rotation angles. Crystallographic results for low molecular weight compounds show that deviations greater than 10" from trans planarity are rare for ester groups.J. COR~IBERT, N. V. MIEN, F. BRISSE et R. H. MARCHESSAULT. Can. J. Chem. 52,3742 (1974). On a determine la conformation cristalline de la polypivalolactone par analyse des energies conformationnelles de chaines; on a trouve que l'tnergie minimum correspond a une conformation trans coplanaire pour le groupe ester. Ce rCsultat est compare avec les donnees de rayons-)< publiees, basees sur la diffraction de fibre, qui montrent une deviation notable de la planarite trans. On discute de cette difference en termes d'knergies relatives impliquees et par comparaison avec les resultats cristallographiques rapportes dans la litterature pour des esters carboxyliques de faible poids moleci~laire. On fait remarquer que, dd ail peu d'information de la diffraction des fibres, la consideration d'energie internee est importante pour attribuer les angles de rotation interne. Les resultats cristallographiques pour des composes de bas poids moleculaires montrent que des deviations plus grandes que 10' par rapport a la planarite traits sont rares dans les groupes esters.[Traduit par le journal]

Structures of Mixed-Tacticity Polyhydroxybutyrates

“…They correspond, via Bragg's equation, to measures of 0.88 nm > d > 0.44 nm, larger than interatomic distances, but matching interchain distances in iso-PHB. 23 The average interchain distances in amorphous PHB can be expected to be of the same order; oscillations around which determine the broadness of the amorphous pattern. 27 Because of the lack of long-range order, no higher-angle diffraction intensities, which would result from higher Miller index lattice planes, are observed.…”

Intermolecular vibrational modes of crystalline Poly-(r)-3-Hydroxybutyrate observed at Terahertz frequencies investigated by molecular dynamics

“…1(a)shows the chemical structure of PHB, which has been determined by the wide-angle x-ray diffraction measurement [50]. It was reported that the unit cells of PHB belong to the orthorhombic system, P2 1 2 1 2 1 (D 2 4), (α = β = γ =90 o ) with a=5.76 Å, b=13.20 Å, c=5.96 Å (fiber repeat) [50,51]. In our system we have considered super cell (a×4, b×2, and c×4) keeping the same lattice parameter.…”

Rotamers arising from restricted motions and electromc interactions of acetoxymethyl groups in carbohydrates

“…It seeins well established that the barr~er to rotatlon around the former 1s very high and that only small departures from planarity of the ester group are poss~ble (7,8). The conformat~on around the C(6)-O(6) bond can be rat~onal~zed on the basls of non-bonded and electrostat~c Interact~ons alone.…”