Transcript Chapter 9 – Compounds of Carbon

Chapter 9 – Compounds of
Carbon
Bonding in Carbon Compounds
• Carbon’s electron configuration is 1s22s22p2.
• It is in period 2, group 14 of the periodic table, meaning it
has four outer electrons and is a small atom.
• The carbon atom forms covalent bonds by sharing these
electrons with other atoms.
• Carbon forms strong covalent bonds with hydrogen atoms,
and nearly all organic molecules contain hydrogen bonded
to carbon.
• Carbon also forms strong covalent bonds with other carbon
atoms, forming long chains and rings.
• Single, double or triple bonds can form between carbon
atoms.
Bonding in Carbon Compounds cont…
• When four single bonds are formed around a
carbon atom, the pairs of electrons in each
bond act as a charge cloud.
• These charge clouds repel each other, so that
they spread out as far away from each other
as possible.
• This arrangement is called a tetrahedral
arrangement.
Homologous Series
• Homologous series are where the compounds
have similar structures and chemical
properties and the same general formula.
• Each member of a homologous series differs
by a CH2 group from the previous member.
Alkanes
• Has the general formula of CnH2n+2.
• The alkanes are called saturated hydrocarbons
because they do not react further with
hydrogen.
• Only single carbon bonds are present.
Cyclic Molecules
• A chain of carbon atoms can also be bent
round to form a ring.
• Molecules formed in this way are called cyclic
molecules.
Cyclic Molecules cont…
• Sometimes, like in the case of benzene, three
of the four outer shell electrons from each
carbon atom form normal covalent bonds but
the fourth electron is shared (delocalised)
around the six-membered carbon ring.
• In all there are 6 delocalised electrons being
shared by the six carbon atoms.
• Compounds like this with rings of delocalised
elecrons are known as arenes.
a Benzene has delocalised electrons.
b A shorthand representation of the benzene
molecule.
c The delocalised electrons are sometimes
represented by these structures.
Isomers
• Molecules of alkanes that contain less than
four carbon atoms, have only one possible
structure.
• Form butane onwards, there are different
arrangements of atoms that share the same
formula.
• These are called structural isomers.
• Structural isomers have different physical and
chemical properties.
Naming Alkanes
• The first part of the name indicates the
number of carbon atoms.
• The last part ends in ane, to indicate there are
only single bonds.
• In isomers, the side chain can be considered
as an alkane that has lost a hydrogen atom.
• The fragment that forms the side chain is
known as an alkyl group.
Naming Isomers
• The name of the longest alkane hydrocarbon
chain.
• The name and number of any alkyl side chains
• The position of the side chain on the main
carbon chain.
Naming Isomers cont…
• The systemic name usually contains a prefix, a
stem and a suffix.
• The name of the hydrocarbon can be
determined as follows:
1. Identify the longest chain of carbon atoms. The
carbon atoms in this chain are numbered.
2. Check bonding, ane for single bonds.
3. Identify the side chain and the number of the
carbon atom on the longest chain to which it is
attached. Numbering always starts on the end of
the chain closest to a side chain.
Alkenes
• Hydrocarbons with double covalent bonds between
carbon atoms are called alkenes.
• The general formula of alkenes is CnH2n
• Hydrocarbons that contain double or triple bonds are
unsaturated hydrocarbons.
• These substances are more reactive than alkanes.
• The shape of the alkenes around the double bond is
planar.
• The angles around these bonds are 120 degrees.
• Carbon atoms not involved in the double bond still
have the tetrahedral orientations.
Alkenes cont…
• The names of alkenes end in ene.
• The stem of the systematic name of alkenes is
based on the longest chain that contains the
double bond.
• The position of the double bond is indicated
by the number of the first carbon atom
involved in the double bond..
• The rules for naming these chains are similar
to those for alkanes.
Functional Groups
• Carbon can also form covalent bonds with other
atoms or groups of atoms.
• These are called functional groups.
• A functional group is an atom or a group of atoms
that gives a characteristic set of chemical properties
to a molecule containing that group.
• Many compounds can be produced by substituting a
hydrogen atom in an alkane molecule with different
functional groups.
• The remaining fragment of the alkane, which has one
hydrogen atom removed, is called an alkyl group,
represented by R.
Functional Groups cont…
• The bonds formed between
carbon atoms and between
carbon and hydrogen atoms are
strong and relatively
unreactive.
• Functional groups located in
different positions in a
molecule result in structural
isomers.
• Where needed, a number can
be used to show where the
functional group is attached to
the carbon chain.
Chloroalkanes
• It is possible to replace a hydrogen atom in an alkane with a
chlorine, to form a chloroalkanes.
• The systematic name for a chloroalkane starts with chloro
followed by the name of the alkane.
• In chains higher than two carbons it is possible to put
chlorines on different carbons.
• In this case, numbers are used to indicate where the chlorine
is.
• The names of alkyl groups are also included in the name.
• The other halogens fluorine, bromine and iodine form similar
homologous series to the chloroalkanes.
Name this chloroalkane…
Alkanols
• Alkanols is the systematic name for the group
of chemicals commonly called alcohols.
• Alkanols have the general formula of ROH.
• The hydroxyl functional group –OH has been
substituted for one hydrogen atom.
• Alcohols are more soluble in water and have
higher boiling points than alkanes.
Alkanols cont…
• Alkanols are named by dropping the e at the
end and replacing it with ol.
• In higher members of this series, the –OH
functional group may be placed at the end or
middle of the carbon chain.
• Numbers are used to indicate the position of
the functional group.
Carboxylic Acids
• Carboxylic acids contain the carboxyl functional group.
• The general formula is RCOOH.
• Bonds within this functional group are polarised, resulting in
the formation of hydrogen bonds between molecules or
between carboxylic acid molecules and water.
• The stem of the systematic name of the carboxylic acids is
determined by the number of carbon atoms in the longest
chain that contains the COOH group.
• The e is taken off the end, when naming, and replaced by oic.
• Branched carboxylic acids are named in a similar way to the
other branched organic compounds.
Name this carboxylic acid…
Amines
• Organic compounds that contain the –NH2 functional
group are called amines.
• The general formula for the amine homologous series is
RNH2.
• These are named by replacing the e at the end of the
name of the alkane with amine.
• The bonds around the nitrogen atom are polar due to the
high electronegativity of nitrogen.
• Smaller amines are very soluble in water due to the
formation of hydrogen bonds.
• The solubility decreases as the size of the alkyl group
becomes larger.
Amino Acids
• Are the basic building blocks for proteins.
• The contain the amine and carboxylic acid
functional groups.