A Study on the Relative Stabilities of Selected Isomers of 1,3-Dimethyl-2,4-Pyrimidinedione and 2,4-Pyrimidinedione. The Effect of The Molecular Environment on Selected Lactim-Lactam Equilibria

The first experimentally based estimates for the relative stabilities in the vapor phase of 2,4-pyrimidinedione (1), 2,4-dihydroxypyrimidine (6), 4-hydroxy-(1H)-2-pyrimidone (3) are for 1-6 -22 (+OR-) 8.8 kcal/mole and for 1-3 -19 (+OR-) 6 kcal/mole. These values were derived from the free energies of isomerization of the methyl analogues 1,3-dimethyl-2,4-pyrimidinedione (7)-2,4-dimethoxypyrimidine (12) of -38 (+OR-) 4.2 kcal/mole and 4-methoxy-1-methyl-2-pyrimidone (9)- 7 of -27 (+OR-) 4.1 kcal/mole. The free energies of isomerization in the vapor for the methyl systems 12-7 and 9-7 were obtained by calorimetric measurement of the heats of isomerization in the neat liquids of -44 (+OR-) 2.6 and -24 (+OR-) 1.3 kcal/mole respectively and subsequent conversion to the gas phase with estimated heats of vaporization. It is noted that in these systems the energy differences between the dilactim or lactim and the dilactam structure was much greater than the energy difference between the dilactim and lactim structures. This behavior is qualitatively rationalized in terms of the delocalization energy present in the dilactam structures due to the presence of a second carbonyl. The comparison of the experimentally calculated relative stabilities of 6-1 and 3-1 with those calculated by molecular orbital methods showed none of the theoretical calculations to be satisfactory.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• White, James Matthew

• Chemistry, Organic

Identifier

(UMI)AAI8209644

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70186