CH 12 alkanes

What is a sigma bond?

The result of the overlap of 2 orbitals. Each carbon atom in an alkane is joined to 4 other atoms by single covalent bonds.

Why does boiling point increase down the alkane homologous series?

• as chain length increases, molecules have larger surface area so more surface contact

• London forces become greater so more energy required to overcome forces

Equation for complete combustion of methane

CH4(g) + 2O2(g) > CO2(g) + 2H2O(l)

Equation for reaction of methane with bromine

CH4(g) + Br2(l) > CH3Br(g) + HBr(g)

What are the mechanism steps for bromination of alkanes?

1. Initiation

2. Propagation

3. Termination

what is the mechanism for bromination of alkanes

radical substitution

write the equation for the first stage in the mechanism of bromination of methane

Br2(g) > 2 Br*

Isomer

Compounds that have the same molecular formula but their atoms are arranged differently

Structural isomer

Compounds that have the same molecular formula but different structural formula

Chain isomer

Same functional group but a different carbon chain

Position isomer

Same functional group in a different position

Functional group isomer

Same molecular formula with different functional group

What effect does branching have on boiling points for alkanes?

Lower boiling point as less points of surface contact between molecules so fewer London forces.

Equations for the second mechanism stage in bromination of methane

1. Ch4 + Br* > CH3* + HBR

2. CH3 + Br2 > CH3BR + BR*

Equations for the 3rd mechanism stage for the bromination of methane

Br* + Br+ > Br2

CH3 + Br* > CH3Br

Effect of chain length on boiling point in alkanes

As increases, molecules have larger surface area so more points of contact between molecules. London forces will be greater and more energy required to overcome forces.