Related Experiment Video
Updated: Jul 16, 2026

In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework
Published on: February 1, 2020
Stereochemistry of beta-deuterium isotope effects on amine basicity
Charles L Perrin1, Brian K Ohta, Joshua Kuperman
1Department of Chemistry 0358, University of California, San Diego, La Jolla, California 92093-0358, USA. cperrin@ucsd.edu
Abstract:
Secondary beta-deuterium isotope effects on amine basicities are measured using a remarkably precise NMR titration method. Deuteration is found to increase the basicity of methylamine, dimethylamine, benzylamine, N,N-dimethylaniline, 2-methyl-2-azanorbornane, and pyrrolizidine. The increase in dimethylamine arises entirely from enthalpy, contrary to a previous report. The method permits a determination of intramolecular isotope effects in 1-benzyl-4-methylpiperidine and 2-benzyl-2-azanorbornane. It is found that deuteration has a larger isotope effect when either antiperiplanar or synperiplanar to a lone pair, but the synperiplanar effect is smaller, as confirmed by computations. The isotope effect is attributed to a lowered zero-point energy of a C-H bond adjacent to an amine nitrogen, arising from delocalization of either a syn or an anti lone pair, and with no detectable angle-independent inductive effect.
Related Concept Videos
Exceptions to the Octet Rule
Acid Strength and Molecular Structure
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
Alkyl Halides
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...
Inductive Effects on Chemical Shift: Overview
Basicity of Aliphatic Amines
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates higher...
Basicity of Heterocyclic Aromatic Amines

