Chapter 13, Problem 35P

Interpretation Introduction

Interpretation:

The stability of propyne and allene on the basis of heat of hydrogenation is to be determined. The reason why isomerization of an allene with a strong base leads to the formation of propyne is to be explained.

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 the halide group and hydrogen group are removed to form alkene is called dehydrohalogenation.

舧 The reaction in which hydrogen is added to the compound in the presence of catalyst is known as hydrogenation.

舧 The number of moles of hydrogen absorbed will be equal to the number of double bonds.

舧 Heat of hydrogenation in unsaturated compounds, like alkenes, conjugated dienes or alkynes, is used to measure the stability of carbon – carbon double bonds in alkenes and conjugated dienes or triple bond in alkynes. By definition, it is the heat produced when hydrogen reacts with unsaturated compounds.

舧 The smaller the numerical value of heat of hydrogenation of an unsaturated bond, the more stable is the unsaturated bond.