13.1 and 13.2
Pi bond (π) A bond formed by the sideways overlap of two p
orbitals, containing two electrons and with the
electron density concentrated above and below the
line joining the nuclei of the bonding atoms.
For each carbon atom of the double bond Three of them are sigma bond, one is a pi bond
how many are pi and sigma bonds?
Properties of a π bond Locks the two carbon atoms in position and
prevents them from rotating around the double
bond.
Draw a diagram showing the formation of
the C=C bond in ethene
Stereoisomerism C=C bonds only. Same structural formula but a
different arrangement of atoms in space
Explain the shape and bond angle of a There are three regions of electron density around
carbon to carbon double bond each of the carbon atoms. The three regions repel
each other as far apart as possible, so the bond
angle around each carbon atom is 120°. All the
atoms are in the same plane.
E/Z isomerism A type of stereoisomerism in which different
groups attached to each carbon of a C=C double
bond may be arranged differently in space because
of the restricted rotation of C=C bond
Cis-trans Isomerism A special type of E/Z isomerism in which there are
two non-hydrogen groups and two hydrogen atoms
around the C=C double bond. The cis isomer (Z)
has hydrogen atoms on each carbon on the same
side whilst the trans isomer (E isomer) has
hydrogen atoms on each carbon on different sides.
What two conditions must a molecule meet A C=C double bond
to have E/Z isomerism? Different groups attached to each carbon atom of
the double bond
, Draw the displayed and skeletal formulas of
but-2-ene- both stereoisomers
Using the Cahn-Ingold-Prelog rules If the groups of higher priority (ie higher atomic
describe how you know whether a molecule number) are on the same side of the double bond,
is the E or Z isomer the compound is the Z isomer. If the groups of
higher priority are diagonally placed across the
double bond, the compound is the E isomer.
Use the atom that is directly attached to the carbon
atoms of the double bond.
What so you do if the two atoms attached to Find the first point of difference. The group which
carbon atom in the double bond are the has the higher atomic number at the first point of
same? difference is given the higher priority.
H CH2 Z
3 CH2
CH CH2
Cl
CH2
OH
Which type of isomer?
13.3
Name the four reactants that react with Hydrogen
alkenes in addition reactions, the reactions Halogens
of which need to know Hydrogen halides
Steam in the presence of an acid catalyst
Conditions for hydrogenation of alkenes In the presence of a nickel catalyst, 423k
Conditions for halogenation of alkenes Chlorine or bromine at room temperature
Conditions for hydrogen halide reaction with React with gaseous hydrogen halides at room
alkenes, what does it form temperature to form haloalkanes
Describe the test for unsaturation When bromine water (an orange solution) is added
dropwise to a sample of an alkene, bromine adds
across the double bond. The orange colour
disappears, indicating the presence of a C=C bond
Pi bond (π) A bond formed by the sideways overlap of two p
orbitals, containing two electrons and with the
electron density concentrated above and below the
line joining the nuclei of the bonding atoms.
For each carbon atom of the double bond Three of them are sigma bond, one is a pi bond
how many are pi and sigma bonds?
Properties of a π bond Locks the two carbon atoms in position and
prevents them from rotating around the double
bond.
Draw a diagram showing the formation of
the C=C bond in ethene
Stereoisomerism C=C bonds only. Same structural formula but a
different arrangement of atoms in space
Explain the shape and bond angle of a There are three regions of electron density around
carbon to carbon double bond each of the carbon atoms. The three regions repel
each other as far apart as possible, so the bond
angle around each carbon atom is 120°. All the
atoms are in the same plane.
E/Z isomerism A type of stereoisomerism in which different
groups attached to each carbon of a C=C double
bond may be arranged differently in space because
of the restricted rotation of C=C bond
Cis-trans Isomerism A special type of E/Z isomerism in which there are
two non-hydrogen groups and two hydrogen atoms
around the C=C double bond. The cis isomer (Z)
has hydrogen atoms on each carbon on the same
side whilst the trans isomer (E isomer) has
hydrogen atoms on each carbon on different sides.
What two conditions must a molecule meet A C=C double bond
to have E/Z isomerism? Different groups attached to each carbon atom of
the double bond
, Draw the displayed and skeletal formulas of
but-2-ene- both stereoisomers
Using the Cahn-Ingold-Prelog rules If the groups of higher priority (ie higher atomic
describe how you know whether a molecule number) are on the same side of the double bond,
is the E or Z isomer the compound is the Z isomer. If the groups of
higher priority are diagonally placed across the
double bond, the compound is the E isomer.
Use the atom that is directly attached to the carbon
atoms of the double bond.
What so you do if the two atoms attached to Find the first point of difference. The group which
carbon atom in the double bond are the has the higher atomic number at the first point of
same? difference is given the higher priority.
H CH2 Z
3 CH2
CH CH2
Cl
CH2
OH
Which type of isomer?
13.3
Name the four reactants that react with Hydrogen
alkenes in addition reactions, the reactions Halogens
of which need to know Hydrogen halides
Steam in the presence of an acid catalyst
Conditions for hydrogenation of alkenes In the presence of a nickel catalyst, 423k
Conditions for halogenation of alkenes Chlorine or bromine at room temperature
Conditions for hydrogen halide reaction with React with gaseous hydrogen halides at room
alkenes, what does it form temperature to form haloalkanes
Describe the test for unsaturation When bromine water (an orange solution) is added
dropwise to a sample of an alkene, bromine adds
across the double bond. The orange colour
disappears, indicating the presence of a C=C bond
