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www.thisisrevision.com for tests, flashcards and revision courses www.thisisrevision.com for tests, flashcards and revision courses Preparation of metal chlorides (not explicitly Edexcel C2000 but useful) Structural isomerism – molecules to be familiar with. Iron (II) chloride: Pass dry HCl gas over heated iron filings. Fe(s) + 2HCl(g) ➜ FeCl2(s)+ H2 (g) Iron (III) chloride: Pass dry Cl2 gas over heated iron filings. 2FeCl3(s) 2Fe(s) + 3Cl2(g) ➜ Aluminium chloride: Pass dry Cl2 gas over heated aluminium foil. 2AlCl3 (s) 2Al(s) + 3Cl2(g) ➜ Draw the structural isomers of C 4H10O that are alcohols. CH3CH2CH2CH 2OH CH3CH2CH(OH)CH 3 (CH3)3COH CH3CH(CH3 )CH2OH butan-1-ol butan-2-ol 2-methyl propan-2-ol 2-methyl propan-1-ol These chlorides must be prepared under anhydrous conditions because water will hydrolyse them to hydroxides. The apparatus used is the sublimation chamber. The CaCl2 guard tube on the exit can be replaced with KOH to absorb unreacted gases if a fume cupboard is not available. Dry CaCl2 Also the ethers, CH 3CH2OCH2CH3, CH3CH2CH2OCH3 and CH3CH(CH3)OCH3? Gas out To what extent do the above molecules differ from one another physically? Dry CaCl2 Gas in Fe filings or Al foil metal chloride sublimate Keep cold to condense product Heat Amongst the alcohols, branching lowers the boiling points because the intermolecular hydrogen bonding becomes hindered and because branching decreases surface area, weakening the induced dipole forces. The alcohols have higher boiling points than the ethers, because the alcohols possess hydrogen bonding and the ethers do not. Isomerism – definitions and basic ideas. Geometrical isomers Isomers are different molecules made from the same set of atoms, or molecular formulae. CH3 Structural isomers have the same molecular formula but a different structural formula, i.e. the atoms are connect up in a different order. • • • Butane CH3CH2CH2CH3 and methyl propane CH3CH(CH3)CH3 are chain isomers, they have different carbon chains. This is also known as branch isomerism. 1-bromo butane CH3 CH2CH2CH2Br and 2-bromo butane CH3CH2CHBrCH3 are positional isomers. They differ in the position of an atom or group (here the Br atom) along an otherwise identical carbon chain. Ethanol CH3CH2OH and methoxymethane CH3OCH3 are functional group isomers, they differ by having different functional groups. Stereo isomers have the same molecular formula and the same structural formula, differing only in the spatial arrangement of their bonds. • • Cis but-2-ene and the trans isomers differ by having methyl groups arranged either on the same side (cis), or opposite sides (trans), this is an example of geometrical isomerism. 2-hydroxypropanoic acid exists as two non-superimposable mirror images, this is an example of optical isomerism. www.thisisrevision.com for tests, flashcards and revision courses H C CH3 C H CH3 C H CH3 C H Why can the above molecules exhibit geometrical isomerism? • • • There is no free rotation about the C=C bond, due to sideways overlap of p orbitals. Neither carbon atom has two identical groups attached. Groups can be arranged either on the same (cis) or opposite (trans) side of the double bond. The restriction of rotation does not always have to be caused by a C=C bond. Geometrical isomerism can occur in cyclic structures, for example 1,2-dichlorocyclopropanes, 2,4dinitrophenyl hydrazines and some transition metal complexes, such as PtCl2(NH3)2. NH 3 H3N H 3N Pt Cl Cl cis Cl Pt Cl NH 3 trans www.thisisrevision.com for tests, flashcards and revision courses