Theoretical study of substituent effects on the geometry and strain enthalpy in [2,2]paracyclophanes

Abstract

The substituent effect on the geometry and strain enthalpy of [2,2]paracyclophane is theoretically investigated by density functional theory. Gas-phase calculations were performed for twenty distinct electron donating and electron withdrawing substituents. The largest out-of-plane distortion of phenyl rings is exhibited by —SCN and —CF3 groups. On the other hand, —OH, —CH3 and —F groups show the minimal deformation. The strain enthalpy for unsubstituted [2,2]paracyclophane associated with repulsive forces between phenyl units reached up to 118.5 kJ mol−1. Any substitution causes increase of the strain enthalpy value proportionally to the absolute values of Hammett para-substituent constants. Two separate linear dependences with similar slopes were obtained for monosubstituted as well as double symmetrically substituted derivatives.

What Is the Main Feature Distinguishing the Through-Space Interactions in Cyclophanes from Their Aliphatic Analogues?

“…The aim of our present study is a comparison of the through-space interaction and some through-bond interactions in typical cyclophanes with two benzene rings where one benzene ring is joined with an aliphatic unit, [ n ]­cyclophanes and araliphanes as well as aliphatic analogues of cyclophanes where both benzene rings have been replaced with alicyclic ones. As the “reference system”, we have taken a typical cyclophane, widely investigated I [2.2]­paracyclophane − (Scheme ). The other typical cyclophanes analyzed are II metapara[2.2]­cyclophane, anti -[2.2]­metacyclophanes IIIa and IIIb , ,, and syn -[2.2]­metacyclophane IIIc .…”

“…We have undertaken investigation of the geometry, atomic charges, mobility of the electrons in the molecule, energy of the interactions between the benzene ring and aliphatic unit, steric strain, and the attractive and repulsive through-space interactions for compounds presented in Scheme . The typical cyclophanes I – III − and [ n ]­cyclophanes VI – IX , were the object of previous investigation, but in order to perform a reliable comparative study of the different groups of cyclophanes, analysis of properties using the same method of calculation seems to be desirable. The crystal structure of compounds V, X , and XI and the derivative of XII were known, but the intramolecular interactions have not been an object of investigations up to now.…”