Chemistry - further organic chemistry

  • Created by: med95
  • Created on: 25-04-13 13:29


  • Structuarl isomerism is branching on a molecule
  • Steriosomers differ in their 3D shape
  • Geometric isomers are across a double bond - cis/trans
  • Optical iosmerism is a type of stereoisomerism - if 2 objects are mirror images and non-superimposable then they are chiral and show optical isomerism
  • Chrial centre- when 4 different groups are bonded to a central atom e.g. carbon - it is non-symmetrical
  • The two different isomers are said to be enantoimers of each other labelled D and L- you cannot superimpose L onto D
  • Enantomiers have similar chemical and physical properties and cannot be told apart by them
  • The difference between enantomiers is their effects on plane polorised light - one enantomier rotates it clockwise +, the other anti-clockwise -
  • If compounds have different effects on plane polorised light they are said to be optically active
  • Biological systems are very sensitive to different optical isomers
  • Normal light is unpolorised and its oscillations can take place in many different planes
  • Plane polorised light - where wave oscillations occur only in one plane
  • The optical activity of an enantomier is measured by the number of degrees it rotates plane polorised light
  • Some solutions of optical isomers have no effect on plane polorised light as there is an equal mix 1:1 ratio of the + and - enantomiers - a racemic mixture so cancel each other out
  • SN2 reactions - substitution, nucleophilic, 2nd order inverts the molecule
  • SN1 reactions have a slow first rate determining step in which a carbocation is formed - at this time the molecule is planar so the attacking nucleophile is equally likely to attack from above or below - hence a racemic mixture is formed

Aldehydes and ketones

  • Aldehydea and ketones have a carbonyl group C=O
  • In an alkene with a C=C there is a pi and sigma bond and as both the carbons have the same electronegativity then the bond is not polarand electron density is equally distributed
  • In a carbonyl group the electrons are distributed evenly between the O and C as O is more electronegative then C so C becomes delta +ive and 0 delta -ive creating a permanatly polorised bond
  • Aldehydes can be produced from the oxidation of a primary alcohol
  • Ketones can be produced from the oxidation of a secondary alcohol
  • The carbonyl group affects the physical propeties in aldehydes and ketones and more so in short chains
  • While the carbonyl group does not allow H bonds it can form permanent dipole -dipole interactions so aldehydes and ketones have higher melting points than alkanes who only have van der waals but lower than alcohols that are able to form H bonds
  • Straight chained aldehydes/ketones can pack closer together than branches ones so the forces between molecules in a straight chain isomers are stronger than in branched isomers so straight chains have higher boiling points
  • Both carbonyl compounds have distinct smells and can be used as artificial flavourings
  • Miscibility decreases with increasing chain length
  • They can be miscible as although they…


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