Chemistry 2A/2B, Term 4 Notes B
1
Coghlan
Chemistry 2A/2B – Term 4, Notes B
Alkenes
Alkenes are ____________ ____________ and contain at least one ____________ bond.
Name
Formula
State
Ethene
C2 H4
Gas
Propene
C3 H6
Gas
Butene
Pentene
Hexene
Heptene
Octene
Nonene
Decene
General formula for the alkenes: CnH2n
Structural formula
Chemistry 2A/2B, Term 4 Notes B
2
Coghlan
Naming of the alkenes
The double bond’s ____________ should always be given unless the name is
____________.
e.g. 2, 3, 3 – trimethyl – 1 – butene
2, 3, 4, 5 – tetramethyl - 3 - hexene
It is possible to get alkenes with 2 ____________ bonds - ..diene, 3 double bonds - ..
____________ etc.
e.g. 1, 3 - butadiene
Isomerism with Alkenes
Just as with the alkanes (position ____________ isomerism or chain ____________), the
alkenes show isomerism (same ____________ formula but different ____________
formula). Because of the lack of ____________ of the C atoms about a ____________
bond, ____________ isomerism can occur.
e.g. cis – dichloroethene
trans – dichloroethene
Chemistry 2A/2B, Term 4 Notes B
3
Coghlan
cis – 2 - pentene
trans – 2 – pentene
cis – 2 – butene
trans – 2 – butene
http://www.chemguide.co.uk/basicorg/isomerism/geometric.html
Exercise
Write names for the following;
Reactions – chain and cyclical alkenes
1. Combustion – just the same as for ____________.
In excess oxygen
In limited oxygen
Chemistry 2A/2B, Term 4 Notes B
4
Coghlan
2. Addition
The alkenes are more ____________ than the alkanes - the double bond is a site of
____________ and species will be added on both ____________ of the double bond as it
collapses to a ____________ bond. During addition reactions the unsaturated compound
will become ____________.
Hydrogenation
e.g.
Halogenation
e.g. Test for double bond – decolourisation of bromine water
Hydrohalogenation
e.g.
Hydration
e.g.
Note: The non-hydrogen atoms usually ____________ to the the C atom with the initially
____________ number of Hs (Markovnikoff’s rule).
EC Set 33
Chemistry 2A/2B, Term 4 Notes B
5
Coghlan
Alkynes
Alkynes are ____________ hydrocarbons and contain at least one ____________ bond.
Name
Formula
State
Ethyne
C2 H2
Gas
Propyne
C3 H4
Gas
Structural formula
Butyne
etc……
General formula for the alkynes: CnH2n-2
Naming of the alkynes
The triple bond’s ____________ should always be given unless the name is
____________.
e.g. 1, 4, 5 – trichloro – 2 – pentyne
http://library.thinkquest.org/3659/orgchem/alkenes-alkynes.html
Note:
1 – heptyne
2 – heptyne
3 – heptyne
3 – heptyne The numbering system must be changed here.
2 – heptyne
1 – heptyne
Chemistry 2A/2B, Term 4 Notes B
6
Coghlan
Exercise
Write names for the following;
Alicyclic Hydrocarbons
These are hydrocarbons in which the Cs are arranged in ____________ ring
____________. ____________ is not counted as one of these compounds.
Cycloalkanes
- C – C – (CnH2n)
Cycloalkenes
- C = C – (CnH2n-2)
Cycloalkynes
-C≡C-
(CnH2n-4)
The aklicyclics are name by adding the prefix ____________ to the normal name.
Theoretically there are no limits to how many C form the ring but commonly up to 30 Cs
form the ring structure. Cyclo compounds with only 3 or 4 Cs tend to be ____________ .
e.g. cyclohexane
____________ ≡
cyclopentane ≡
____________ ≡
1, 2 – dichloro – 3 – iodocyclohexane
Chemistry 2A/2B, Term 4 Notes B
7
Coghlan
e.g. 3 – chloro – 4 – methyl – 1 – cyclopentene
Exercise:
Reactions
Alicyclic compounds exhibit the same ____________ as their ____________ chain
____________ – combustion, ____________ and addition.
e.g.
Combustion
Substitution
Addition
Chemistry 2A/2B, Term 4 Notes B
8
Coghlan
Aromatic Hydrocarbons – Benzene
http://www.npi.gov.au/database/substance-info/profiles/12.html
These are ____________ that contain one or more ____________ rings (C6H6). Benzene
does not ____________ undergo ____________ reactions ____________ by alkenes and
____________. This suggests its bonding ____________ is ____________ to both. All
the ____________ in the benzene ring are ____________ and this is indicated by
benzene’s symbol
As expected, the aromatics have low m.p., low ____________ ,
low ____________ and are ____________. These properties can be explained by the low
____________ forces between ____________.
Isomers
Aromatic exhibit ____________ structural ____________.
e.g. 1, 2 – dimethylbenzene
1, 3 – dimethylbenzene
1, 4 – dimethylbenzene
Reactions
Chemistry 2A/2B, Term 4 Notes B
9
Coghlan
Benzene’s reactions are typically ____________ however benzene will ____________ to
form CO2 and H2O. In air the combustion forms copious quantities of ____________
smoke.
Combustion
e.g.
Halogenation
e.g.
Nitration
e.g.
Alkylation
e.g.
Empirical Formulae
Ex/ Complete combustion of 19.4 g of a hydrocarbon was found to produce 58.7 g of
carbon dioxide. If its molar mass is 58.1 g mol-1, calculate its molecular formula.
Chemistry 2A/2B, Term 4 Notes B
10
Coghlan
Ex/ 100.0 mL of oxygen was added to 11.5 mL of a gaseous hydrocarbon. The mixture
was sparked and cooled to original temperature (25.0 oC) and was found to have a volume
of 77.0 mL. This gas mixture was then bubbled through a NaOH solution which dissolved
the CO2. The remaining gas had a volume of 42.5 mL and ignited a glowing splint.
Determine the empirical formula of the hydrocarbon.