Structure and Bonding in Alkenes Questions

Structure and Bonding in Alkenes

Alkenes Worksheet

1. Drawing Skeletal Formulae

Draw the skeletal formulae of the following molecules.
a. But-1-ene

Answer:

Skeletal formula of But-1-ene
b. But-2-ene

Answer:

Skeletal formula of But-2-ene
c. Z-pent-2-ene

Answer:

Skeletal formula of Z-pent-2-ene
d. E-pent-2-ene

Answer:

Skeletal formula of E-pent-2-ene
e. E-2-hydroxybut-2-ene

Answer:

Skeletal formula of E-2-hydroxybut-2-ene
f. Z-2-hydroxybut-2-ene

Answer:

Skeletal formula of Z-2-hydroxybut-2-ene

2. Nomenclature

Name the following molecules.
a. Molecule A

Methylpropene (or 2-methylpropene)

b. Molecule B

Hex-2-ene

c. Molecule C

3,3-dimethylbut-1-ene

d. Molecule D

Pent-2-ene

3. Stereoisomerism

Some of the molecules above display stereoisomerism.
a. State the definition of the term stereoisomerism.

Definition:

Stereoisomerism is when two or more molecules have the same structural formula but a different arrangement of atoms in space.

b. Explain the key feature of an alkene that means that it can form geometric isomers.

Restricted Rotation

There is restricted rotation around the C=C double bond (due to the presence of the π-bond).

4. Structural Isomerism & Properties

Hexene and 2-methylpentene have the same molecular formula but different structural formulae.
a. State the type of structural isomerism that is present in these molecules.

Chain Isomerism

b. Explain why hexene and 2-methylpentene have different boiling points.

Surface Area and Van der Waals Forces

Although both molecules have the same molecular formula (and same number of electrons), hexene is a straight chain while 2-methylpentene is branched.

Hexene molecules can pack closer together, resulting in a larger surface area of contact. This leads to stronger Van der Waals forces between hexene molecules compared to the branched 2-methylpentene, requiring more energy to overcome.

c. Neither hexene nor 2-methylpentene are soluble in water. Explain why this is the case.

Solubility Energetics

Alkenes are non-polar molecules and can only form weak Van der Waals forces with other molecules.

Dissolving them in water would require breaking the strong hydrogen bonds between water molecules. The energy required to break these Hydrogen bonds is not compensated for by the formation of the weak Van der Waals forces between the alkene and the water. Therefore, the process is energetically unfavorable.