Chapter 11+12

Question 1

Formula for an alkane.

Answer 1

CnH2n+2

Question 2

Formula of cycloalkanes/alkenes.

Answer 2

CnH2n

Question 3

What is the definition of structural isomerism?

Answer 3

Compounds with the same molecular formula but different structural formula

Question 4

What is the definition of stereoisomerism?

Answer 4

Compounds with the same structural formula but a different arrangement of atoms in 3D space

Question 5

What is the definition of a sigma bond?

Answer 5

The overlap of atomic orbitals directly between the bonding atoms (single bonds). Each bond has 2 shared electrons. Make alkanes very stable molecules.

Question 6

What 3D arrangement do alkanes form, and with what bonding angle?

Answer 6

Tetrahedral - 109.5*

Question 7

What happens to m/b points of alkanes as no. carbon atoms increases?

Answer 7

M/b point increases as of stronger London forces and molecules have a larger SA so more points of surface contact - so more energy required to overcome them.

Question 8

What happens to m/b point when branching of an alkane increases?

Answer 8

Fewer surface points of contact, leading to fewer and weaker London forces as molecules can’t get as close - so less energy required to overcome them.

Question 9

Apart from complete/incomplete combustion what other reaction do alkanes take part in?

Answer 9

With Halogens. Radical substitution under presence of UV light. Starts with initiation (formation of radicals via homolytic fission), propagation, then termination (two radicals collide forming a molecule with all electrons paired).

Question 10

What are two limitations of radical substitution?

Answer 10

1. Further substitution (haloalkane product forms a dihaloalkane with another Br radical etc until all H’s are replaced).
2. Can substitute at different positions in carbon chain to give a range of products (not efficient).