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Hydrocarbons BIOB111 Session 8 (Saturated Hydrocarbons (ALKANES (C…
Hydrocarbons
BIOB111
Session 8
Saturated
Hydrocarbons
contains maximum number of H atoms
saturated
with H atoms
ALKANES
C atoms arranged in an open chain (straight or branched)
molecular formula = CnH2n+2
functional group
Nomenclature
identify longest continuous C chain (trunk)
this is the parent hydrocarbon
how many C atoms does it have - prefix
where do the functional group/s attach?
what is the functional group that is attaching - name this
number longest chain beginning at the end nearest to the first branch point
Physical
properties
non-polar
no difference in the polarity or the ability to attract electrons within the compound
equal sharing of electrons - both equally attracted to the electrons
insoluble in water (water is polar)
soluble in non-polar solvents (chloroform, benzene)
lower density than water
low boiling point
boiling point increases as molecular weight and number of C atoms increase
branched alkanes have lower BPs than straight chained alkanes
cycloalkanes have higher boiling points than alkanes with the same number of C atoms
CYCLOALKANES
cyclic saturated hydrocarbons
C atoms arranged into a closed ring structure
restricts free rotation of bonded carbons
Chemical
properties
Combustion
exothermic reaction with O2 producing CO2, H2O and heat
Redox reaction
Halogenation
Group VII
periodic table
direct reaction with halogens
substitution of one/more H atoms by halogen = haloalkanes or halocycloalkanes
Chlorofluorocarbons
Unsaturated
Hydrocarbons
#
#
1 or more double or triple covalent bonds between C atoms
unsaturated
with H atoms
more chemically reactive than saturated hydrocarbons -
double and triple bonds are easily broken
Structural
formulas
condensed structural formula
line-angle formulas
expanded structural formula
IUPAC
nomenclature
Prefix
1 = meth-
2 = eth-
3 = prop-
4 = but-
5 = pent
6 = hex
Suffix
single bond = -ane
double bond = -ene
triple bond = -yne
ALKENES
Chemical
Reactions
Polymerisation
many alkenes form popylmer chains
reaction between monomer units removes double bonds
catalyst used to initiate polymerisation
Addition
reactions
convert alkenes to alkanes
Hydrogenation
addition of a H2 molecule
additional of a small symmetrical molecule
H atoms added to each C that forms the multiple bond
Halogenation
addition of X2 (Cl2, Br2)
addition of a small symmetrical molecule
Hydrohalogenation
HBr or HCl
Markovnikov's Rule
- in the addition of an HX to an alkene, the H attaches to the C that has fewer alkyl substituents, and the X attaches to the C that has more alkyl substituents
Hydration
addition of H2O molecule
Combustion
double bond is very reactive
unsaturated hydrocarbons containing 1 or more double bond
functional group
molecular formula = CnH2n
Polyenes
alkenes with 2 or more C=C bonds
alkadienes - 2 C=C
alkatrienes - 3 C=C
Cis-Trans
isomerism
same molecular formula, same order of atom attachment but different arrangement of atoms in space
CYLCLOALKENES
cyclic unsaturated hydrocarbons containing 1 or more C=C bonds within the ring structure
ALKYNES
unsaturated hydrocarbons containing 1 or more triple bonds
functional group
Physical Properties
#
#
molecular formula = C2H2n-2
Chemical
Reactions
triple bond is very reactive
Addition
reactions
#
same as Alkenes
hydrogenation of alkynes produces alkenes
further hydrogenation of alkenes produces alkanes
AROMATIC
HYDROCARBONS
ARENES
Benzene and its derivatives
form side groups by removing 1 H atom
called phenyl/aryl functional group
many arenes (compounds containing the benzene ring) are fragrant - responsible for aroma of plants
BENZENE
C6H6
benzene unreactive
behaves like an alkane
resonance structures
Resonance provides stability through delocalisation of electrons
the 3 double bonds in the cyclic structure of benzene are formed by 6 electrons
these 6 electrons are equally shared by all the 6 C atoms of the benzene ring = very stable
