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Topic 10 (Strand 7: Trends in Physical Properties (Recap of Intermolecular…

- - - - Dipole–dipole forces (or attractions) only exist between polar molecules that have a permanent dipole.
    - - Hydrogen bonding occurs between molecules that have an electronegative nitrogen, oxygen or fluorine atom directly bonded to a hydrogen atom.
    - - London dispersion forces exist between all molecules and atoms. They are the reason why noble gases such as helium can be liquefied at very low temperatures (–269 oC).
- - - - 1 meth-
      - 2 eth-
      - 3 prop-
      - 4 but-
      - 5 pent-
      - 6 hex-
  - - - As with the alkenes, use a number to show the position of the carbon≡carbon triple bond once the longest carbon chain is composed of four or more atoms (using the lowest number possible).
    - - Carboxylic acids contain the carboxyl functional group (COOH). They are named using the prefixes Meth Eth etc with the suffix -anoic acid. The first member of the carboxylic acid homologous series is methanoic acid (HCOOH).
    - - It becomes necessary to use a number once the longest carbon chain is composed of three or more carbon atoms; as always, use the lowest number possible. Note that branched-chain alcohols are named in a similar way to branched-chain alkanes where the side-chain is assigned a number and prefix
    - - When naming alkenes with more than four carbon atoms in the longest chain, use a number to show the position of the carbon=carbon double bond; number the carbon atoms to obtain the lowest number
    - - straight chains
        
        Straight-chain alkanes are named by counting the number of carbon atoms in the longest carbon chain (which gives the prefix) and adding the suffix -ane.
      - branched chains
        
        Three steps
        
        Identify the longest continuous carbon chain in the molecule. This gives the stem of the name.
        
        Identify and name the side-chains or substituent groups; these give the prefix of the name. If there is more than one side-chain of the same type, use the prefixes di-, tri-, tetra- and so on. If a molecule contains several different side-chains, list them in alphabetical order.
        
        Identify the position of the side-chain(s), using a number which refers to the number of the carbon atom in the stem. The carbon atoms in the carbon chain are numbered starting from the end which will give the substituent groups the lowest number.
        
        Name of side-chain (R group) Condensed structure
        
        methyl –CH3
        
        ethyl –CH2CH3
        
        propyl –CH2CH2CH3
        
        butyl –CH2CH2CH2CH3
    - - Ethers are volatile solvents composed of two alkyl groups bonded by an oxygen atom. Their volatility arises from the fact that they are unable to form hydrogen bonds between molecules, because they lack an oxygen directly bonded to a hydrogen atom. This inability to form hydrogen bonds also explains why ethers do not mix with water: the ether molecules cannot form hydrogen bonds with water molecules.
      - When naming ethers, the shorter alkyl group is given the prefix alkoxy- (methoxy- or ethoxy-, for example) and the longer alkyl group is given the name of the corresponding alkane
    - - Aldehydes are named using the prefixes and the suffix -anal. The first member of the series, with one carbon atom, is methanal (HCHO).
      - Ketones are named using the prefixes and the suffix -anone (note that first ketone in the homologous series is propanone). When naming ketones with more than four carbon atoms, numbers are used to indicate the position of the carbonyl group (C=O) in the molecule.
    - - Nitriles are derived from carboxylic acids with the carboxyl group (COOH) replaced by a nitrile group (C≡N). When naming nitriles, the carbon atom of the nitrile group counts as the first atom of the hydrocarbon chain, and the suffix -nitrile is added.
      - Amines contain the amine functional group (−NH2). This group can be attached to a hydrocarbon chain in a similar way to a halogen atom or a hydroxyl group. Amines can be classified as primary, secondary or tertiary, depending on how many alkyl groups are bonded to the nitrogen atom of the amine group. Primary amines have one alkyl group, secondary amines have two and tertiary three. Primary amines are named using the prefixes followed by the suffix -amine
      - Secondary amines are named on the basis of the longest unbranched carbon chain bonded to the nitrogen atom of the amine group. The second alkyl group is named using the prefix methyl-, ethyl- propyl-, etc., with an italicised N.
      - Tertiary amines have two alkyl groups bonded to the nitrogen atom of the amine group, each using an italic N
      - Amides are derivatives of carboxylic acids in which the -OH group has been replaced by a -NH2 group. When naming amides, the -oic suffix of the carboxylic acid is replaced by -amide. For example, the primary amide with four carbon atoms is named butanamide, with the molecular formula CH3CH2CH2CONH2. Secondary and tertiary amides are named in the same way as the amines
- - - - Look at images to see the difference between Pentane and 2methlybutane.
    - - Positional Isomers form when the functional group is attached in different positions.
    - - The isomers have the same molecular formula but different functional groups.