A theoretical study of substituted 2-butanones and their enols

Dissertant

al-Maayitah, Nuha Suwaylim

Thesis advisor

Khalil, Salim Muhammad

Comitee Members

al-Umari, Hamzah
Mahasinah, Ali

University

Mutah University

Faculty

Faculty of Science

Department

Department of Chemistry

University Country

Jordan

Degree

Master

Degree Date

2002

English Abstract

The present work is divided in two parts: the First part is to study the effect of perfluorination on keto-enol tautomerism of 2-butanone and enol counterparts, and also the effect of inserting one and two fluorine atoms at different positions on the 2-butanone and enol counterparts.

The second Part is to study the effect of other substituents such as CF3, N02, CN, NC, CH3, NH2, O" at (a-position) on the 2-butanone and enol counterparts.

MINDO- Forces method was used to calculate heats of formation, electron densities and charge distributions with complete optimization of geometry of all compounds.

MNDO method was used to calculate the entropies of all compounds.

The subsituents affect the geometrical parameters (bond lengths and angles) especially at the position where the substituent is attached.

The stabilizing effects of substituents on 2-butanone and enol counterparts were determined by thermodynamic calculations (Gibbs free energy) and isodesmic reactions.

First part: The calculated heats of formation (AHf) of 2-butanone I and 2-buten-2-ol 2 are -58.151 kcal/mol and -58.529 kcal/mol, respectively, i.e.

2-butanone i is less stable than its enol counterpart by 0.378 kcal/mol.

While the calculated heat of formation (AHf) of 1-buten-2-ol 3 is -53.677 kcal/mol i.e.

2-butanone 1 is more stable than its enol counterpart by 4.474 kcal/mol.

This is supported by calculation of Gibbs free energy (AG) between ketone 1 and enol 2 which was found to be -0.779 kcal/mol i.e.

reaction is spontaneous which means enol 2 is slightly stable than Ketone J_.

This is in agreement with published experimental results.

In the case of perfluorination of keto-enol system, perfluorination destabilized ketone greater than enol, this is supported by isodesmic reaction and Gibbs free energy Value.

For stepwise fluorination of keto-enol system, it was found that as the number of fluorine atoms increases the stability of the enol form increases relative to the keto form.

Second part: The effect of substituents such as N02, CF3, CN, NC, NH2, CH3, O" have been studied on 2-butanone.

Two enol counterparts are formed.

The first enol (la) has the substituent attached to the double bond and the second enol (lb) has the substituent attached to carbon adjacent to the double bond.

OH O OH 1 A • ! /** • •' s\ • (la) (1) (lb) It is found that the substituents O", NH2, act as strong electron releasing subsitituents while CF3 and NO2 act as strong electron withdrawing substituents.

The CN, NC and CH3 groups were found to act as weak electron releasing groups.

Introduction of the substituents O", NH2, CF3, N02, CN, NC, CH3 to keto-enol system increase the stability of enol from (la) and gave negative AG value which indicates the stabilization of enol.

The stability of enol la is a rise from the interaction between electrons of the double bond and the 7i* orbital of the substituents.

It was found that the stability of keto-enol system depends on the substituted group (releasing or with drawing).

The strong electron with drawing group such as CF3, N02 were found to destabilized ketone more than the rest the substituents group.

Main Subjects

Chemistry

No. of Pages

134

Table of Contents

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Language

English

Data Type

Arab Theses

Record ID

BIM-303513