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

Abstract

Two reversible solid-state phase transitions of erucic acid (cis-13-docosenoic acid), the γ f R and γ1 f R1 phase transitions, have been followed by vibrational spectroscopy (IR and Raman) and X-ray diffraction. The crystal structure analyses of the higher temperature phases, R and R1, have been performed. The symmetry of crystal lattices remains unchanged during the both transitions, i.e., the γ and R phases belong to a monoclinic system (P2 1 /a) and the γ1 and R1 phases belong to a triclinic one (P1 h). At the γ f R transition point, the subcell structure of the methyl-terminal chains is reconstructed, accompanying a large conformational change of cis-olefin groups. On the γ1 f R1 transition, the inclination manner of hydrocarbon chains changes, while there are no significant changes in the subcell structure and the conformation of cis-olefin groups. The conformational disorder at methyl terminals increases continuously for the γ1 f R1 transition, contrary to an abrupt occurrence at the γ f R transition. The unit cell volume also increases gradually in the γ1 and R1 phases and shows no prominent changes at the γ1 f R1 transition, while a stepwise increase takes place at the γ f R transition. The important factors for transition behaviors are discussed on the basis of the crystal structures.

Phase behaviour of transkarbam 12

“…With increasing temperature, the intensity of this band decreases and another band appears at 870 cm −1 , which is assigned to the CH 3 rocking mode of disordered chain end conformations (Kaneko et al, 1996). In the melt, the CH 3 rocking modes form a broad background (see Fig.…”

“…3a and b) assigned according to the literature are summarized in Table 1 (Dollish et al, 1973;Snyder et al, 1978;Snyder, 1979;Snyder and Scherer, 1979;Brown Dollish et al (1973), Snyder et al (1978), Snyder (1979), Snyder and Scherer (1979), Kobayashi et al (1986), Brown et al (1987), Lin-Vien et al (1991), and Kaneko et al (1996Kaneko et al ( ). et al, 1987Lin-Vien et al, 1991;Kaneko et al, 1996).…”

“…The conformationally and packing dependent Raman modes of hydrocarbon chains such as CH 2 stretching, CH 2 scissoring, CC stretching, and CH 3 rocking bands have been described in detail in the literature (Snyder et al, 1978;Snyder, 1979;Snyder and Scherer, 1979;Kobayashi et al, 1986;Brown et al, 1987;Kaneko et al, 1996;Wegener et al, 1996). IR spectroscopy is a suitable technique used to characterize the polar head groups of lipid molecules (Rerek et al, 2001).…”

Martensitic Phase Transition of Petroselinic Acid: Influence of Polytypic Structure

“…The dihedral angles should change from 157, 0, -160 to 91, 1, 130°(molecule A) or to 127, 1, 119°(molecule B), but the large potential barriers for this conformation change is not so large. 24 Owing to this flexibility of the cis-olefin group, the structural change of subcell from O⊥ to M// in the methyl-terminal chain does not need large displacements of the carboxyl-terminal chains. Now we compare the LM f HM transition with the E f C transition of stearic acid (n-C 18 acid) that exhibits no martensitic transition.…”

Polymorphic behavior of gondoic acid and phase behavior of its binary mixtures with asclepic acid and oleic acid

“…The γ and α forms exhibit a reversible transformation, where aliphatic conformation of the ω chain transforms from ordered (γ) to disordered (α) on heating. Yet, the ordered conformation of the ∆-chain does not change, keeping an O′ // subcell unchanged (10). Here, the ωand ∆chains refer to the segments of the aliphatic chains between a methyl end group and the double bond and the segment be-tween the double bond and a COOH group, respectively.…”