title: The interplay between hydrogen bonding and π-π stacking interactions in the crystal packing of N1-thyminyl derivatives, and implications for the photo-chemical [2π + 2π]-cycloaddition of thyminyl compounds.
abstract: The solid-state photo-chemical dimerisation of thyminyl derivatives occurs when two thyminyl units are aligned in such a way that the olefinic moieties are separated by a distance of less than 4.2 Å. When irradiated with >270 nm UV, the thyminyl olefinic groups undergo [2π + 2π]-cycloaddition to form a dimeric cyclobutane derivative. However, the design and execution of [2π + 2π]-cycloaddition reactions can be challenging due to the requirement to produce molecular crystals with the necessary olefinic alignment. In this investigation, the crystallographic and solid-state photo-chemical reactions of six N1-thyminyl derivatives are studied. Only one derivative, thyminyl propanamide (), was found to undergo [2π + 2π]-cycloaddition in the crystalline state. As such, quantum chemical methods were employed to study the photo-chemical transition states of the derivatives, as well as the strengths of typical intermolecular interactions that were observed in their crystal structures (such as π-π stacking between the thyminyl rings, Watson and Crick style hydrogen bonding and hydrogen bonding between functional groups of N1 substituents). These results were used to rationalise the solid-state photo-reactivity of more complex bis-thyminyl monomers.
authors.affiliation: Centre for Green Chemistry, Monash University, Clayton, Australia.
authors.forename: Priscilla
authors.initials: P
authors.lastname: Johnston
authors.forename: Ekaterina I
authors.initials: EI
authors.lastname: Izgorodina
authors.forename: Kei
authors.initials: K
authors.lastname: Saito
mesh_terms: D018360:Crystallography, X-Ray; D061565:Cycloaddition Reaction; D019281:Dimerization; D006860:Hydrogen Bonding; D008968:Molecular Conformation; D011789:Quantum Theory; D013816:Thermodynamics; D013941:Thymine / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D014466:Ultraviolet Rays
chemical_list: D013941:Thymine