12 Alkanes

radical

a species w an unpaired electron

reaction mechanism for chlorine + ethane

alkanes

saturated hydrocarbons, containing only carbon and hydrogen atoms, joined w single convalent bonds

sigma bond σ

the result of the overlap of two orbitals, one from each bonding atom

single bond in alkanes

do σ sigma bonds have rotation

yes, they are not rigid

what shape would u expect around the C atoms in alkanes

tetrahedral

• carbon has 4 bonding regions which r filled so 4 bond pairs

• equal repulsion

diagram for 3D shape of ethane

what process does crude oil undergo to extract alkanes

fractional distillation

what r fractions

a mixture of similar length hydrocarbons

where is the fractionating column the hottest

bottom

coldest at top

describe steps of fractional distillation

• crude oil fed into column and vaporised (bitumen never vaporises tho)

• rises and condenses in trays in fractions when its bpt is reached

cracking

the shortening of longer chained alkanes to make shorter, more useful chains

how does branching have an effect on bpt of alkanes

more branching = lower bpt

• less branching means molecules are closer together

• higher SA in contact

• greater LF and IMF

• more energy required to pull molecules apart

characteristics of small alkanes

• low bpt

• runny, low viscosity

• easy to ignite, flammable

• burns w clean flame

characteristics of big alkanes

• high bpt

• viscous

• hard to ignite

• burns w smoky flame

y do characteristics of alkanes change w increase in chain length

• longer chain

• more electrons

• greater LF

• more energy required to overcome LF

• combustion tends to be less complete (smoky flame)

y don’t alkanes react w most common reagents

• C-C and C-H sigma bonds r v strong

• C-C bonds r non polar

• electronegativity of C and H is so similar the C-H bond is considered non-polar

y are alkanes used as fuels

• readily available

• easy to transport

• burn in a plentiful supply of oxygen w/out releasing toxic products

what do alkanes need to react w halogens and y

sunlight

the high energy UV radiation present provides the initial activation energy needed for the rxn to take place

what kind of reaction is bromination of alkanes

substitution

photochemical

which halogens will react w alkanes

bromine and chlorine

iodine isn’t reactive enough, fluorine too reactive

what is the mechanism for bromination of alkanes

radical substitution

steps for radical substitution

1. initiation

2. propagation

3. termination

what r the limitations w radical substitution in organic synthesis

• multiple organic compounds are formed

• if C chain is longer than 2, a mixture of monosubstituted isomers will be made

reactions of alkanes

• combustion

• cracking

• alkanes + halogens in sunlight

radical

what is a reactive intermediate that acts as a catalyst in alkanes + halogens in UV

radical

features of homologous series

• each successive member differs by a CH2 group

• similar chemical properties, gradually differing physical properties

• same general formula

• same functional group

describe how a sigma bond forms

overlap of orbitals directly between the bonding atoms