Alkanes

Question 1

Alkanes formula

Answer 1

CnH2n+2
SATURATED (all single bond)

Branched chain are formed by alkyl grps (CnH2n+1)

Cyclo alkanes CnH2n

Question 2

Physical properties of alkanes & BP of alkane isomers

Answer 2

Alkanes have SMS, low amt of energy needed to overcome weak idid betw moleqs

Branched have lower bp than straight chain
eg. Pentane straight, 2,2-dimethylpropane branched
- Surface area of contact pentane >2,2 dimethpropane
- Pentane has greater extent of distortion of e- cloud
- Greater extent of idid, more energy req to overcome

Question 3

Alkane solubility

Answer 3

SOLUBLE in NON POLAR solvent
energy released from formation of idid betw alkane moleq & non-polar solvent moleq sufficient to overcome idid betw alkane solute solute & solvent solvent

INSOLUBLE in POLAR
Energy released from formation of idid betw alkane & H2O moleq insufficient to overcome idid betw alkane moleq (solvent-solvent) & H bonds betw H2O (solute-solute)

Question 4

Why are alkanes unreactive?

Answer 4

1. Saturated & non-polar
2. Do not contain region of low or high e- density -> unreactive towards polar reagents, do not attract electrophiles & nucleophiles

Question 5

Alkane rxns

Answer 5

Free radical substitution***
Combustion
Alkenes undergo reduction (catalytic hydrogenation) to give alkanes

Question 6

What are free radicals?

Answer 6

Highly reactive species due to unpaired e- formed by homolytic fission

Question 7

What is homolytic fission?

Answer 7

(Half headed arrow)
Breaking of covalent bond betw 2 atoms
Each atom retains ONE shared e- forming RADICALS

Question 8

What is heterolytic fission?

Answer 8

(Full headed arrow)
Breaking of a covalent bond betw 2 atoms so 1 atom retains both shared e- forming IONS