Unit 10
tructure 3.2: Functional groups: Classification of organic compounds
S
.2.1: Empirical, molecular and structural formula
3
- Organic compounds can be represented by different types of formulas. These include empirical, molecular, structural (full and
condensed) and skeletal.
- A structural formula is one that shows unambiguously how the atoms are arranged together. A full structural formula shows every
atom and bond
- A condensed structural formula can omit bonds between atoms and can show identical groups bracketed together
- A skeletal formula is an even more shorthand way to show a structure. It shows the carbon ‘skeleton’ with any functional groups,
omitting all hydrogen atoms.
● Identify different formulas and interconvert molecular, skeletal and structural formulas.
● Construct 3D models (real or virtual) of organic molecules.
3.2.2: Functional groups
- Functional groups give characteristic physical and chemical properties to a compound. Organic compounds are divided into classes
according to the functional groups present in their molecules.
- A functional group is the reactive part of the molecule which gives its characteristic properties
- Carbon atoms are unable to expand their octet which also makes them very stable
● Identify the following functional groups by name and structure: halogeno, hydroxyl, carbonyl, carboxyl, alkoxy, amino, amido, ester,
phenyl.
- Halogeno group (-X) in a halogenoalkane
- Hydroxyl group (-OH) in alcohols
- Carbonyl group (-CO) in aldehydes and ketones
- Carboxyl group (-COOH) in carboxylic acids
- Alkoxy group (-O-) in ethers
- Amino group (-NH2) in amines
- Amido group (-CONH2) in amides
- Ester group (-COO) in esters
- Phenyl group (-C6H 5) in arenes
3.2.3 and 3.2.4: Homologous series
- A homologous series is a family of compounds in which successive members differ by a common structural unit, typically CH2. Each
homologous series can be described by a general formula.
- A homologous series is a series of organic compounds which can be grouped together based on similarities in their structure and
reactions. They have the same general formula
- They have similar chemical properties and show gradation in their physical properties
● Identify the following homologous series: alkanes, alkenes, alkynes, halogenoalkanes, alcohols, aldehydes, ketones, carboxylic acids,
ethers, amines, amides and esters.
- S uccessive members of a homologous series show a trend in physical properties.
- escribe and explain the trend in melting and boiling points of members of a homologous series.
D
- The molar mass of the compound
- The molar mass of each member of the series increases by roughly the same amount.
- The strength of the London dispersion forces between the molecules depends on the contact surface area between
the molecules.
, - Larger molecules with a higher molar mass have a greater constant surface area and stronger London dispersion
forces.
- So, as the molar mass increases, the strength of the London dispersion forces also increases and so do the melting
point and boiling point.
- The structure of the molecule: whether it is straight-chain or branched.
- The branches prevent the molecules from getting close together, which results in less surface area contact
between the molecules and weaker London dispersion forces.
- The straight-chain molecules can get closer together, which results in a greater surface area contact and
stronger London dispersion forces.
- This explains why a straight-chain molecule has a higher boiling point than a branched-chain molecule.
- The functional group present in the molecule, which has an effect on the polarity of the molecule.
- Longer chains of hydrocarbons tend to become less soluble
- Non-polar compounds such as the alkanes, alkenes and alkynes will only have London dispersion forces acting
between their molecules and tend to have lower boiling points, in other words they are more volatile.
- Polar compounds such as aldehydes and ketones have not only London dispersion forces acting between their
molecules but also dipole–dipole attractions. This results in these compounds having higher boiling points than
non-polar organic compounds of similar molar mass.
- Compounds with either N–H or O–H bonds, such as the alcohols, carboxylic acids, amines and amides, have hydrogen
bonds acting between their molecules. Because hydrogen bonds are the strongest type of intermolecular force,
these compounds tend to have higher boiling points and are the least volatile.
- ow useful are 3D models (real or virtual) to visualize the invisible?
H
They are useful for understanding certain base concepts like what bonds to what and how many bonds are needed in a compound, they
also help differentiate between structural isomers better than drawings do. However they miss out things like polarity due to the
natural way they twist and turn making it difficult to see whether they are straight chained or not. They can also get very
complicated and harder to use when the compounds get bigger.
3.2.5: Naming organic compounds
- “IUPAC nomenclature” refers to a set of rules used by the International Union of Pure and Applied Chemistry to apply systematic
names to organic and inorganic compounds.
● Apply IUPAC nomenclature to saturated or mono-unsaturated compounds that have up to six carbon atoms in the parent chain and
contain one type of the following functional groups: halogeno, hydroxyl, carbonyl, carboxyl.
- Alkane and halogenoalkane: -ane
- alkene: -ene
- alkyne: -yne
- Alcohols: -anol
- Aldehyde: -anal
- Ketone: -anone
- Carboxylic acid: -anoic acid
- Ether: -oxyalkane
- Amine: -anamine
- Amide: -anamide
- Ester: connected to the single bond O is -yl and connected to the double bond O is -anoate
- Arene: -benzene
Note that
, ● Include straight-chain and branched-chain isomers.
● Include numeric prefixes (mono, di, tri, tetra, penta, hexa).
- In order to describe completely an organic molecule, three features must be described:
1) the longest straight carbon chain on the molecule.
a) The longest straight chain on the molecule is indicated by one of the prefixes meth-, eth-, prop-, but-, pent- and
hex-
2) the length and position of any branches on the molecule.
a) Many carbon chains are not straight chains but are branched. The presence of a branch is indicated one of the
following prefixes: methyl, ethyl, hydroxy-, amino-, fluoro-, chloro-, bromo-, iodo-, phenyl-
b) The position of the branch must be specified according to the number of the carbon on the straight chain to which it
is attached. (2-methylbutane, 2,3-dimethylpentane, 1,1,2-trichloropropane)
c ) T he carbons are always numbered from the carbon at the end of the chain closest to the functional group.
) If there is no functional group, the carbons are numbered from the carbon at the end of the chain closest to the
d
ranch.
b
3) the nature and position of any functional groups on the molecule.
a) The priority functional group (the one that affects its properties the most) is the end of the name of the compound.
3.2.6: Structural isomers
- Structural isomers are molecules that have the same molecular formula but different connectivities (arrangement of atoms).
● Recognize isomers, including branched, straight-chain, position and functional group isomers.
- In structural isomerism, the atoms are arranged in a completely different order. There can be differences based on the chain,
the position of a functional group or even the functional group itself. (an isomer can be an alcohol or ether)
● Primary, secondary and tertiary alcohols, halogenoalkanes and amines should be included
- Primary:the C-OH/C-X/C-NH2 is attached to 0 or 1other carbon atoms. In other words, they are molecules in which the
functional group is at the end of the chain.Example:propan-1-ol, 1-chloropropane, propan-1-amine
- Secondary:the C-OH/C-X/C-NH2 is attached to 2 othercarbon atoms (only one H atom). They are molecules in which the
functional group is not at the end of the chain.Example:propan-2-ol, 2-chloropropane, propan-2-amine
- Tertiary:the C-OH/C-X/C-NH2 is attached to 3 othercarbon atoms (no H atoms). The functional group is attached to a
c arbon which also has a branch attached to it.Example:2-methyl propan-2-ol, 2,2-chloromethyl propane, 2-methyl
propan-2-amine
3.2.7: Stereoisomers
- Stereoisomers have the same constitution (atom identities, connectivities and bond multiplicities) but different spatial arrangements
of atoms.
● Describe and explain the features that give rise to cis-trans isomerism; recognize it in non-cyclic alkenes and C3 and C4
cycloalkanes.
- These isomers occurs where you have restricted rotation somewhere in a molecule
- Cis- means the isomer has both groups on the same side of the molecule
- Trans- means the isomer has the groups on different side of the molecule
- Free rotation is not possible in a c=c bond (due to the position of the p orbitals in the pi bond)
- When carbon atoms are joined in a ring, the bond angles are strained and free rotation is not possible.
- Groups or atoms attached to the ring can be in the cis- or trans- position relative to the plane of the ring
- Note that it does not matter which carbon atom the groups are joined to, it is their position relative to the plane of the ring
that determines whether they arecis-ortrans-isomers
tructure 3.2: Functional groups: Classification of organic compounds
S
.2.1: Empirical, molecular and structural formula
3
- Organic compounds can be represented by different types of formulas. These include empirical, molecular, structural (full and
condensed) and skeletal.
- A structural formula is one that shows unambiguously how the atoms are arranged together. A full structural formula shows every
atom and bond
- A condensed structural formula can omit bonds between atoms and can show identical groups bracketed together
- A skeletal formula is an even more shorthand way to show a structure. It shows the carbon ‘skeleton’ with any functional groups,
omitting all hydrogen atoms.
● Identify different formulas and interconvert molecular, skeletal and structural formulas.
● Construct 3D models (real or virtual) of organic molecules.
3.2.2: Functional groups
- Functional groups give characteristic physical and chemical properties to a compound. Organic compounds are divided into classes
according to the functional groups present in their molecules.
- A functional group is the reactive part of the molecule which gives its characteristic properties
- Carbon atoms are unable to expand their octet which also makes them very stable
● Identify the following functional groups by name and structure: halogeno, hydroxyl, carbonyl, carboxyl, alkoxy, amino, amido, ester,
phenyl.
- Halogeno group (-X) in a halogenoalkane
- Hydroxyl group (-OH) in alcohols
- Carbonyl group (-CO) in aldehydes and ketones
- Carboxyl group (-COOH) in carboxylic acids
- Alkoxy group (-O-) in ethers
- Amino group (-NH2) in amines
- Amido group (-CONH2) in amides
- Ester group (-COO) in esters
- Phenyl group (-C6H 5) in arenes
3.2.3 and 3.2.4: Homologous series
- A homologous series is a family of compounds in which successive members differ by a common structural unit, typically CH2. Each
homologous series can be described by a general formula.
- A homologous series is a series of organic compounds which can be grouped together based on similarities in their structure and
reactions. They have the same general formula
- They have similar chemical properties and show gradation in their physical properties
● Identify the following homologous series: alkanes, alkenes, alkynes, halogenoalkanes, alcohols, aldehydes, ketones, carboxylic acids,
ethers, amines, amides and esters.
- S uccessive members of a homologous series show a trend in physical properties.
- escribe and explain the trend in melting and boiling points of members of a homologous series.
D
- The molar mass of the compound
- The molar mass of each member of the series increases by roughly the same amount.
- The strength of the London dispersion forces between the molecules depends on the contact surface area between
the molecules.
, - Larger molecules with a higher molar mass have a greater constant surface area and stronger London dispersion
forces.
- So, as the molar mass increases, the strength of the London dispersion forces also increases and so do the melting
point and boiling point.
- The structure of the molecule: whether it is straight-chain or branched.
- The branches prevent the molecules from getting close together, which results in less surface area contact
between the molecules and weaker London dispersion forces.
- The straight-chain molecules can get closer together, which results in a greater surface area contact and
stronger London dispersion forces.
- This explains why a straight-chain molecule has a higher boiling point than a branched-chain molecule.
- The functional group present in the molecule, which has an effect on the polarity of the molecule.
- Longer chains of hydrocarbons tend to become less soluble
- Non-polar compounds such as the alkanes, alkenes and alkynes will only have London dispersion forces acting
between their molecules and tend to have lower boiling points, in other words they are more volatile.
- Polar compounds such as aldehydes and ketones have not only London dispersion forces acting between their
molecules but also dipole–dipole attractions. This results in these compounds having higher boiling points than
non-polar organic compounds of similar molar mass.
- Compounds with either N–H or O–H bonds, such as the alcohols, carboxylic acids, amines and amides, have hydrogen
bonds acting between their molecules. Because hydrogen bonds are the strongest type of intermolecular force,
these compounds tend to have higher boiling points and are the least volatile.
- ow useful are 3D models (real or virtual) to visualize the invisible?
H
They are useful for understanding certain base concepts like what bonds to what and how many bonds are needed in a compound, they
also help differentiate between structural isomers better than drawings do. However they miss out things like polarity due to the
natural way they twist and turn making it difficult to see whether they are straight chained or not. They can also get very
complicated and harder to use when the compounds get bigger.
3.2.5: Naming organic compounds
- “IUPAC nomenclature” refers to a set of rules used by the International Union of Pure and Applied Chemistry to apply systematic
names to organic and inorganic compounds.
● Apply IUPAC nomenclature to saturated or mono-unsaturated compounds that have up to six carbon atoms in the parent chain and
contain one type of the following functional groups: halogeno, hydroxyl, carbonyl, carboxyl.
- Alkane and halogenoalkane: -ane
- alkene: -ene
- alkyne: -yne
- Alcohols: -anol
- Aldehyde: -anal
- Ketone: -anone
- Carboxylic acid: -anoic acid
- Ether: -oxyalkane
- Amine: -anamine
- Amide: -anamide
- Ester: connected to the single bond O is -yl and connected to the double bond O is -anoate
- Arene: -benzene
Note that
, ● Include straight-chain and branched-chain isomers.
● Include numeric prefixes (mono, di, tri, tetra, penta, hexa).
- In order to describe completely an organic molecule, three features must be described:
1) the longest straight carbon chain on the molecule.
a) The longest straight chain on the molecule is indicated by one of the prefixes meth-, eth-, prop-, but-, pent- and
hex-
2) the length and position of any branches on the molecule.
a) Many carbon chains are not straight chains but are branched. The presence of a branch is indicated one of the
following prefixes: methyl, ethyl, hydroxy-, amino-, fluoro-, chloro-, bromo-, iodo-, phenyl-
b) The position of the branch must be specified according to the number of the carbon on the straight chain to which it
is attached. (2-methylbutane, 2,3-dimethylpentane, 1,1,2-trichloropropane)
c ) T he carbons are always numbered from the carbon at the end of the chain closest to the functional group.
) If there is no functional group, the carbons are numbered from the carbon at the end of the chain closest to the
d
ranch.
b
3) the nature and position of any functional groups on the molecule.
a) The priority functional group (the one that affects its properties the most) is the end of the name of the compound.
3.2.6: Structural isomers
- Structural isomers are molecules that have the same molecular formula but different connectivities (arrangement of atoms).
● Recognize isomers, including branched, straight-chain, position and functional group isomers.
- In structural isomerism, the atoms are arranged in a completely different order. There can be differences based on the chain,
the position of a functional group or even the functional group itself. (an isomer can be an alcohol or ether)
● Primary, secondary and tertiary alcohols, halogenoalkanes and amines should be included
- Primary:the C-OH/C-X/C-NH2 is attached to 0 or 1other carbon atoms. In other words, they are molecules in which the
functional group is at the end of the chain.Example:propan-1-ol, 1-chloropropane, propan-1-amine
- Secondary:the C-OH/C-X/C-NH2 is attached to 2 othercarbon atoms (only one H atom). They are molecules in which the
functional group is not at the end of the chain.Example:propan-2-ol, 2-chloropropane, propan-2-amine
- Tertiary:the C-OH/C-X/C-NH2 is attached to 3 othercarbon atoms (no H atoms). The functional group is attached to a
c arbon which also has a branch attached to it.Example:2-methyl propan-2-ol, 2,2-chloromethyl propane, 2-methyl
propan-2-amine
3.2.7: Stereoisomers
- Stereoisomers have the same constitution (atom identities, connectivities and bond multiplicities) but different spatial arrangements
of atoms.
● Describe and explain the features that give rise to cis-trans isomerism; recognize it in non-cyclic alkenes and C3 and C4
cycloalkanes.
- These isomers occurs where you have restricted rotation somewhere in a molecule
- Cis- means the isomer has both groups on the same side of the molecule
- Trans- means the isomer has the groups on different side of the molecule
- Free rotation is not possible in a c=c bond (due to the position of the p orbitals in the pi bond)
- When carbon atoms are joined in a ring, the bond angles are strained and free rotation is not possible.
- Groups or atoms attached to the ring can be in the cis- or trans- position relative to the plane of the ring
- Note that it does not matter which carbon atom the groups are joined to, it is their position relative to the plane of the ring
that determines whether they arecis-ortrans-isomers
