Raman Spectroscopy Determination of ΔH° for the Cis/Trans Isomerization of N-Methylformamide in the Physical Chemistry Laboratory

Abstract

This experiment uses a research grade Raman microscope system to measure the energy difference between the higher energy cisand lower energy trans-isomers of N-methylformamide (NMF). The experimental portion of this work involves measuring the intensities of key Raman bands associated with each of the two isomeric forms of NMF as a function of the temperature. A van't Hoff plot showing the temperature dependence of the equilibrium is used to estimate the standard change in enthalpy (ΔH°) for the reaction. A value of 5.90 ± 0.15 kJ/mol (95% C.I.) for the isomerization of trans to cis was obtained for a set of example data reported. An average over multiple semesters and multiple experimental groups was 6.65 ± 0.86 kJ/mol (s.d.). This compares to four experimental literature values ranging from 3.71−7.44 kJ/mol.