Chemistry - further organic chemistry

Chirality

• 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…