Pyridine–acetaldehyde, a molecular balance to explore the n→π*interaction

Abstract

Weak n→π* and C–H⋯O interactions determine the structure of pyridine–acetaldehyde adduct. The n→π* distance oscillates with the methyl group internal rotation which acts as a sort of molecular balance to explore the n→π* interaction energy.

How Aromatic Fluorination Exchanges the Interaction Role of Pyridine with Carbonyl Compounds: The Formaldehyde Adduct

“…While the C 5 F 5 N experimental structure is reasonably well reproduced by theoretical calculations, the structure of the heterodimer shows evident discrepancies between experiment and DFT or MP2 predictions which could be associated with the difficulties to describe the balance of weak interactions responsible for its formation. However, the experimental structure of the dimer is reproduced to a reasonable agreement by the CCSD/6‐311++G(2d,p) calculations as observed in other complexes formed by weak interactions as pyridine⋅⋅⋅formaldehyde (C 5 H 5 N⋅⋅⋅H 2 CO) [24] or pyridine⋅⋅⋅acetaldehyde (C 5 H 5 N⋅⋅⋅CH 3 CHO) [25] …”

“…However, the experimental structure of the dimer is reproduced to a reasonable agreement by the CCSD/6‐311++G(2d,p) calculations as observed in other complexes formed by weak interactions as pyridine⋅⋅⋅formaldehyde (C 5 H 5 N⋅⋅⋅H 2 CO) [24] or pyridine⋅⋅⋅acetaldehyde (C 5 H 5 N⋅⋅⋅CH 3 CHO). [25] …”

“…In this work, we show how the perfluorination of the pyridine ring completely changes the properties of this system. The interaction of C 5 H 5 N with carbonyl compounds as H 2 CO [24] or acetaldehyde [25] is dominated by a rather strong n→π* interaction with a charge transfer contribution due to the partial delocalization of lone pair of nitrogen into the non‐bonding π orbital of the carbonyl group. The most favorable n→π* interaction should correspond to a N−C‐O angle around 90°.…”

“…In this paper, we present a rotational study of the adduct between pentafluoropyridine and formaldehyde (C 5 F 5 N⋅⋅⋅H 2 CO) as a model of the interaction of the carbonyl group with perfluoro azines. Of additional interest is the fact that the dominant interaction in the complexes of pyridine with carbonylcompounds[ 24 , 25 ] is an n →π* interaction which involves the delocalization of the lone pair ( n ) of pyridine N atom into the antibonding ( π *) orbital of the acceptor carbonyl group. Until now there is no experimental evidence about the possible competition between the lone pair⋅⋅⋅π‐hole and the n →π* interactions.…”

Dynamical Strengthening of Covalent and Non-Covalent Molecular Interactions by Nuclear Quantum Effects at Finite Temperature

“…1-A) [34]. First discussed in early 1970, the n → π * interaction has attracted significant attention in recent years and it is hypothesized to impart substantial structural stability to proteins [35][36][37][38] and molecules [39][40][41][42], as well as define reactivity [40], regulate isomerisation [34] and energy barriers [43], and promote charge transfer [44]. Nevertheless, the actual dynamical implications at finite temperature of such interaction have not been explicitly studied.…”