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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

Form II of DMCA: (a) potentially photoreactive sites; (b) interlocked structure to show the absence of slip planes.
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fig2: Form II of DMCA: (a) potentially photoreactive sites; (b) interlocked structure to show the absence of slip planes.

Mentions: Form II of DMCA crystallizes in the space group P21/n with Z = 4 (Table 1 ▸, Fig. 2 ▸). The primary synthon is the carboxylic acid dimer. These primary modules further interact with each other through C—H⋯O and π⋯π stacking interactions. The closest double bond to double bond mid-point distance between two molecules is 3.574 Å rendering all the DMCA molecules potentially photoreactive (Fig. 2 ▸a). This is in contrast to form I wherein only half the molecules are in a potentially reactive orientation. The arrangement between two closest molecules in a stacked pair is head to tail so that the crystal is of the α-type. A closer inspection of this structure reveals that DMCA molecules are in a syn conformation in contrast to form I where DMCA molecules adopt an anti-conformation. This syn conformation of the DMCA molecule places a restriction on the formation of C—H⋯O interactions between carboxylic acid dimers in the same plane, as is possible in form I and many other trans-cinnamic acids. Because of this restriction, hydrogen-bonded carboxyl dimers in form II are connected to each other through weak out-of-plane C—H⋯O contacts leading to zigzag packing (Fig. 2 ▸b). This difference in packing has major consequences on the mechanical properties of crystals of the two forms: slip planes are possible in form I, these planes in effect being constituted with planar molecules connected with in-plane O—H⋯O and C—H⋯O interactions, whereas form II lacks slip planes and packs in a more isotropic and three-dimensional manner.


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)

Form II of DMCA: (a) potentially photoreactive sites; (b) interlocked structure to show the absence of slip planes.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2: Form II of DMCA: (a) potentially photoreactive sites; (b) interlocked structure to show the absence of slip planes.
Mentions: Form II of DMCA crystallizes in the space group P21/n with Z = 4 (Table 1 ▸, Fig. 2 ▸). The primary synthon is the carboxylic acid dimer. These primary modules further interact with each other through C—H⋯O and π⋯π stacking interactions. The closest double bond to double bond mid-point distance between two molecules is 3.574 Å rendering all the DMCA molecules potentially photoreactive (Fig. 2 ▸a). This is in contrast to form I wherein only half the molecules are in a potentially reactive orientation. The arrangement between two closest molecules in a stacked pair is head to tail so that the crystal is of the α-type. A closer inspection of this structure reveals that DMCA molecules are in a syn conformation in contrast to form I where DMCA molecules adopt an anti-conformation. This syn conformation of the DMCA molecule places a restriction on the formation of C—H⋯O interactions between carboxylic acid dimers in the same plane, as is possible in form I and many other trans-cinnamic acids. Because of this restriction, hydrogen-bonded carboxyl dimers in form II are connected to each other through weak out-of-plane C—H⋯O contacts leading to zigzag packing (Fig. 2 ▸b). This difference in packing has major consequences on the mechanical properties of crystals of the two forms: slip planes are possible in form I, these planes in effect being constituted with planar molecules connected with in-plane O—H⋯O and C—H⋯O interactions, whereas form II lacks slip planes and packs in a more isotropic and three-dimensional manner.

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