Structure of the γ1 phase of erucic acid

Abstract

1060PETROSELINIC ACID ones. Another important factor is the steric hindrance of the bulky carboxyl groups. The parallel orientation of the carboxyl groups is energetically disadvantageous. In the case of n-fatty acid A-super and A2 forms adopting the triclinic subcell with parallel skeletal planes (771), the carboxyl groups take two different orientations in order to reduce the steric hindrance. The formation of an O_l_-like subcell of the HM phase seems to have an analogous effect of promoting the perpendicular packing of carboxyl groups.The thermal factors of the C atoms increase gradually from the cis-olefin group as the methyl terminal is approached. This tendency has been also found in the Yl phase of erucic acid, which shows a reversible phase transition accompanied by conformational disorder at the methyl terminal (Kobayashi & Kaneko, 1990). The thermal motion of the methyl-terminal chains may be activated by the insertion of the cis-olefm group. However, the thermal factor of the methyl C atom is relatively small in comparison to that of the y~ phase. It is inferred that the thermal motion of the methyl-terminal chain is depressed by two factors, the relatively long chain length and the even number of C atoms in the methyl-terminal chain. Petroselinic acid contains three more methylene units in the methyl-terminal chains than erucic acid. The even--odd effect of the number of C atoms on the melting points and crystal structures of nalkanes and n-fatty acids is well known. This dynamical property of the HM phase probably relates to the fact that there is no order-disorder-type phase transition as found in the other cis-monoenic acids.In both molecules A and B, the carboxyl groups are located nearly coplanar to the skeletal planes of the carboxyl-terminal chains.

Phase behavior of mixed systems of SOS and OSO

“…Some additional XRD peaks in the long and short spacing areas are due to the occurrence of more stable forms during sample handling and XRD measure-Flgure 10. Changes of X-ray diffraction spectra of SOS/OSO = 30/70 at (a) 15 °C and (b) 27 °C. ment.…”

“…in the LM form of petroselinic acid {cis-6octadecenoic acid)28 and TH in , of erucic acid. 29 In the case of the HM form of petroselinic acid, the subcell M# is revealed in the chain segment between the double bond and a methyl end group (methyl-sided chain), whereas the carboxyl-sided chain was of the 0_l subcell. In accordance with the difference in the subcell structure, the configuration of the olefin group is different in the above three polymorphs, giving rise to the difference in a total molecular geometry and chain inclination with respect to the lamellar interface.…”

Mechanism of the γ → α and γ1 → α1 Reversible Solid-State Phase Transitions of Erucic Acid

“…Figure 16 clearly indicates that the thermal factors are becoming higher 7) 114.4 (6) 114.2(6) C(6)-C(7)-C (8) 113.0(6) 113.8(6) C(7)-C(8)-C (9) 113.5 (6) 113.3(6) C(8)-C(9)-C (10) 114.0(6) 113.7(6) C(9)-C(10)-C (11) 113.6(6) 113.0(6) C(10)-C(11)-C (12) 114.4 (7) 112.9(7) C(11)-C(12)-C (13) 113.2 (7) 113.0(8) C(12)-C(13)-C (14) 127 179 (4) 176 (4) starting from the 15th carbon atom toward the methyl terminal. Specially large thermal factors around the methyl terminal may reflect the conformational disorders observed in Raman spectroscopy.…”

“…In a previous work we noticed that the transition behavior was rather different between the two reversible phase transitions. 14 For example, the spectral changes of the bands due to cis-olefin group in the γ f R transition are larger than those in the γ1 f R1 transition. We considered that it would be important to investigate the transition behavior of the two transitions in detail and to consider the influences of the crystal structures on the dynamical behaviors of cis-unsaturated acyl chains.…”

“…However, large structural differences exist between the γ and γ1 phases as shown in Figure 1 and Table 1. [14][15] The crystal structure of the γ phase was determined in oleic and erucic acids. 15,16 The unit cell of the γ phase belongs to a monoclinic system (P2 1 /a) containing four molecules, which take the skew-cis-skew′ conformation at the olefin group linked by all-trans polymethylene chains constituting an O′ | subcell.…”