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Crystal chemistry and photomechanical behavior of 3,4-dimethoxycinnamic acid: correlation between maximum yield in the solid-state topochemical reaction and cooperative molecular motion.

Mishra MK, Mukherjee A, Ramamurty U, Desiraju GR - IUCrJ (2015)

Bottom Line: Form I exhibits photosalient behavior but this effect is absent in form II.It is suggested that both Schmidt-type and Kaupp-type topochemistry are applicable for the solid-state trans-cinnamic acid photodimerization reaction.Form II is more brittle, and its interlocked structure seems to favor Schmidt-type topochemistry with minimum molecular movement.

View Article: PubMed Central - HTML - PubMed

Affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science , Bangalore 560 012, India.

ABSTRACT
A new monoclinic polymorph, form II (P21/c, Z = 4), has been isolated for 3,4-dimethoxycinnamic acid (DMCA). Its solid-state 2 + 2 photoreaction to the corresponding α-truxillic acid is different from that of the first polymorph, the triclinic form I ([Formula: see text], Z = 4) that was reported in 1984. The crystal structures of the two forms are rather different. The two polymorphs also exhibit different photomechanical properties. Form I exhibits photosalient behavior but this effect is absent in form II. These properties can be explained on the basis of the crystal packing in the two forms. The nanoindentation technique is used to shed further insights into these structure-property relationships. A faster photoreaction in form I and a higher yield in form II are rationalized on the basis of the mechanical properties of the individual crystal forms. It is suggested that both Schmidt-type and Kaupp-type topochemistry are applicable for the solid-state trans-cinnamic acid photodimerization reaction. Form I of DMCA is more plastic and seems to react under Kaupp-type conditions with maximum molecular movements. Form II is more brittle, and its interlocked structure seems to favor Schmidt-type topochemistry with minimum molecular movement.

No MeSH data available.


Related in: MedlinePlus

A pictorial depiction of the probable mechanism of photoreaction in (a) form I and (b) form II. Arrows represent the directions of movement of molecules during photochemical reaction.
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fig6: A pictorial depiction of the probable mechanism of photoreaction in (a) form I and (b) form II. Arrows represent the directions of movement of molecules during photochemical reaction.

Mentions: If this crystal structure of the (recrystallized) photoproduct bears any relationship to that of the truxillic acid as it is formed in situ in the photoreaction, it would suggest that photodimerization of form II crystals takes place with a minimum of molecular movement and that conversely, photodimerization in form I requires more molecular movement. Under such an assumption, it can also be concluded from Fig. 5 ▸ that there is hardly any movement of the O—H⋯O hydrogen-bonded synthons during the photo-transformation. Of course, half the molecules in the form I crystal are not even organized for a solid-state photoreaction so that it may well be concluded that rather major molecular movements are involved in its photoreaction considering the yield is even as high as 40% (see §3.3). The observation that cracks appear in a perpendicular direction to the main elongation axis of form I may thus be rationalized on the basis of molecular movements as shown in Fig. 6 ▸(a). In contrast, photoreactivity in form II needs only minor adjustments of the structural features (Fig. 6 ▸b).


Crystal chemistry and photomechanical behavior of 3,4-dimethoxycinnamic acid: correlation between maximum yield in the solid-state topochemical reaction and cooperative molecular motion.

Mishra MK, Mukherjee A, Ramamurty U, Desiraju GR - IUCrJ (2015)

A pictorial depiction of the probable mechanism of photoreaction in (a) form I and (b) form II. Arrows represent the directions of movement of molecules during photochemical reaction.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4645110&req=5

fig6: A pictorial depiction of the probable mechanism of photoreaction in (a) form I and (b) form II. Arrows represent the directions of movement of molecules during photochemical reaction.
Mentions: If this crystal structure of the (recrystallized) photoproduct bears any relationship to that of the truxillic acid as it is formed in situ in the photoreaction, it would suggest that photodimerization of form II crystals takes place with a minimum of molecular movement and that conversely, photodimerization in form I requires more molecular movement. Under such an assumption, it can also be concluded from Fig. 5 ▸ that there is hardly any movement of the O—H⋯O hydrogen-bonded synthons during the photo-transformation. Of course, half the molecules in the form I crystal are not even organized for a solid-state photoreaction so that it may well be concluded that rather major molecular movements are involved in its photoreaction considering the yield is even as high as 40% (see §3.3). The observation that cracks appear in a perpendicular direction to the main elongation axis of form I may thus be rationalized on the basis of molecular movements as shown in Fig. 6 ▸(a). In contrast, photoreactivity in form II needs only minor adjustments of the structural features (Fig. 6 ▸b).

Bottom Line: Form I exhibits photosalient behavior but this effect is absent in form II.It is suggested that both Schmidt-type and Kaupp-type topochemistry are applicable for the solid-state trans-cinnamic acid photodimerization reaction.Form II is more brittle, and its interlocked structure seems to favor Schmidt-type topochemistry with minimum molecular movement.

View Article: PubMed Central - HTML - PubMed

Affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science , Bangalore 560 012, India.

ABSTRACT
A new monoclinic polymorph, form II (P21/c, Z = 4), has been isolated for 3,4-dimethoxycinnamic acid (DMCA). Its solid-state 2 + 2 photoreaction to the corresponding α-truxillic acid is different from that of the first polymorph, the triclinic form I ([Formula: see text], Z = 4) that was reported in 1984. The crystal structures of the two forms are rather different. The two polymorphs also exhibit different photomechanical properties. Form I exhibits photosalient behavior but this effect is absent in form II. These properties can be explained on the basis of the crystal packing in the two forms. The nanoindentation technique is used to shed further insights into these structure-property relationships. A faster photoreaction in form I and a higher yield in form II are rationalized on the basis of the mechanical properties of the individual crystal forms. It is suggested that both Schmidt-type and Kaupp-type topochemistry are applicable for the solid-state trans-cinnamic acid photodimerization reaction. Form I of DMCA is more plastic and seems to react under Kaupp-type conditions with maximum molecular movements. Form II is more brittle, and its interlocked structure seems to favor Schmidt-type topochemistry with minimum molecular movement.

No MeSH data available.


Related in: MedlinePlus