Chapter 13, Problem 29P

Interpretation Introduction

Interpretation:

The mechanism for the given reaction between 2,3-dimethyl-1,3-butadiene and hydrogen bromide is to be determined. The reaction energy coordinate diagram that illustrates kinetic and thermodynamic pathways is to be drawn.

Concept introduction:

舧 Electrophiles are electron-deficient species, which has positive or partially positive charge. Lewis acids are electrophiles, which accept electron pair.

舧 Nucleophiles are electron-rich species, which has negative or partially negative charge. Lewis bases are nucleophiles, which donate electron pair.

舧 Free radical is an atom, molecule, or ion that has an unpaired electron, which makes it highly chemically reactive.

舧 Substitution reaction: A reaction in which one of the hydrogen atoms of a hydrocarbon or a functional group is substituted by any other functional group is called substitution reaction.

舧 Elimination reaction: A reaction in which two substituent groups are detached and a double bond is formed is called elimination reaction.

舧 Addition reaction: It is the reaction in which unsaturated bonds are converted to saturated molecules by the addition of molecules.

舧 The reaction in which there is addition of hydrogen molecule is called hydrogenation reaction.

舧 ${\text{H}}_{\text{2}}\text{/Pt}$ is a reducing agent that reduces alkynes to alkanes.

舧 Hydrogenation with platinum as a catalyst is used to convert unsaturated carbohydrates to saturated hydrocarbons

舧 Oxidation of alkenes with ozone in the presence of dimethyl sulphate results in the formation of ketones or aldehydes, depending on the orientation and position of the double bond.

舧 Ozonolysis helps convert the carbon – carbon double bonds to carbon – oxygen double bond (carbonyl compounds).

舧 Dimethyl sulfide is used as a reducing agent that decomposes the intermediate formed into the carbonyl group.

舧 NBS (nitro-bromo succinimide) is a special reagent used for bromination of allylic carbocations.

舧 Bromine replaces the hydrogen attached to the carbon adjacent to the carbon bearing double bond.

舧 This method of using NBS can produce allylic bromides without bromine reacting with the double bond.

舧 Dehydration of a primary alcohol in the presence of a mineral acid like concentrated sulfuric acid results in the formation of alkene via E2 elimination.

舧 1,2–addition of hydrohalogenation (HX) to a diene is the addition of hydrogen to the carbon designated as 1 and halogen to the carbon designated as 2. The positions of carbon as 1 and 2 are not according to the IUPAC numbering of the molecule, but as a conjugated diene. The mechanism is similar to 1,4-addition. The mechanism of 1,2-addition and 1,4-addition of hydrohalogenation is given below:

舧 When conjugated diene is attacked by an electrophile, the resultant products are formed via 1,2-addition and 1,4-addition reaction mechanism. Kinetics and thermodynamics control the reaction and form different products under different reaction conditions.