Chapter 11, Problem 2CP

(a)

Interpretation Introduction

Interpretation:

IUPAC name for isoprene has to be given.

Concept Introduction:

A common nomenclature of naming organic compounds has been developed by IUPAC.  By usage of this nomenclature or rules, memorizing of names of organic compounds is not necessary.

IUPAC rules for naming alkenes:

There are about five rules that has to be followed for naming an alkene and an alkyne.  They are,

• The longest continuous carbon chain in the compound that contains double bond or triple has to be identified.  This is known as parent compound.
• Suffix “–ane” (in name of alkane) is replaced with “-ene” for alkene or “-yne” for alkyne.
• Numbering has to be done so that the lowest number is given to the double or triple bond.
• Naming and numbering has to be given for each atom or group that is attached to the parent chain.  Numbering has to be done in a way that substituents get the least numbering.
• If the alkenes have more than one double bond they are called as alkadienes (two double bonds) or alkatrienes (three double bonds).  Appropriate suffix has to be used depending on the number of multiple bonds present in the compound.

(b)

Interpretation Introduction

Interpretation:

Isoprene will have lower or higher boiling point than 1,4-pentadiene has to be reasoned out.

Concept Introduction:

The force of attraction between two molecules that experience a short-lived dipole is known as London Dispersion force.  Large molecules will have large number of electrons.  These electrons when in constant motion develop a temporary dipole.  The formed temporary dipole interacts with other temporary dipoles resulting in an attractive force between the molecules.  Molecules with a very high molar mass have large number of electrons.  This result in having stronger force of attraction and due to this the melting point and boiling point of the molecule will be higher.