Hammett Linear Free Energy Relationships

What was the reference reaction used by Hammett to determine the substituent constant, σ

• Benzoic acid dissociation

• Sulphuric acid dissociation

• Sodium hydroxide dissociation

• Ester hydrolysis

What does Hammett LFER tells us about a reaction ?

• Possible reaction pathways

• Nature of the intermediate

• Kinetics and thermodynamics relationship of a reaction

• Solvent effect towards a reaction

Answer True or False

When reaction parameter, ρ > 0 indicates the reaction is accelerated by electron withdrawing substituents, therefore aromatic ring has a higher electron density in the transition state than in the starting material

(a)  

In the Hammett plot, the sign of the slope tells whether a reaction rate is accelerated or suppressed by ________________vs. __________________

(a)  

What does the magnitude of ρ in the Hammett equation tells us about a reaction?

• How sensitive a reaction is to the electronic characteristics of the substituent

• How strong is the acid

• How fast the reaction will proceed

• Predicts whether the product formation is favoured or not

The following Hammet plot was obtained for the reaction of dibenzyl chloride with ethanol. Predict which pathway is more likely for the reaction to proceed

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