Fulton content sem1

Heat evolved when a mole of the compound is completely hydrogenated

Usually about 120kJ mol-1 for every double bond

All 6 carbon are sp2 hybridised - each carbon has a p-orbital perpendicular to the plane of the ring. Each of the p orbitals contains a single electron. Partial overlap of the p orbitals allows the electrons to delocalise around the entire ring

Must be cyclic Must be planar Must be cyclically conjugated Must obey huckels rule Must possess an induced ring current when placed in a magnetic field

each atom of the ring(s) must have p-orbital perpendicular to the plane of the ring to allow complete delocalization of the π-electrons

Must possess (4n+2) pi electrons (n=0,1,2 etc) 2,6,10,14 electrons

Induced ring currents in benzene happen when its electrons move in response to an external magnetic field. This creates small currents in the ring structure, causing benzene to be repelled by h (a property called diamagnetism).

The greater the magnetic field experienced, the further downfield those protons appear in the 1H NMR spectrum

Detection of a ring current All aromatic compounds possess a ring current

1) The p-electrons of the ring attack the electrophile to yield a resonance stabilized carbocation - wheland intermediate 2) Substitution is completed by loss of H+

Nitroaromatics can be reduced to aromatic amines Reagent - 1) SnCl2/HCl 2) OH-

Electrophilic is SO3 or HSO3+

To make the reaction go in opposite direction use steam or dilute H2SO4

Halogenating occurs with either Cl2, Br2 or I2 in the presence of a Lewis acid catalyst For bromination use Br2 and FeBr3 For chlorinations use Cl2 and FeCl3 For iodinations use I2 and CuCl2

Friedel crafts alkylation a H is substituted for an alkyl R group Using R-X and AlCl3 Where R-X must be and alkyl halide

i) the alkyl group “activates” the ring towards further attack and the 2nd group substitutes on the ring more easily than the first ii) When primary alkyl halides are used, the electrophile may rearrange to give unexpected products

i) The acyl group has a deactivating influence on the ring and further substitutions are inhibited ii) Ketones can be easily reduced

SOCl2

The rate at which further substitution reactions occur The location at which the next substituent is introduced

Groups like -NH2 and -OH They make the benzene ring more reactive towards electrophilic by donating a pair of electrons, the ring contains more electron density therefore increase the rate of reaction

Groups like -NO2 are deactivating substituents. It makes the benzene ring less reactive towards electrophilic by withdrawing electrons from the ring. The ring contains less electron density therefore decreased rate of reaction

These involve electron donation or electron withdrawal through σ bonds

Negative inductive effects

Positive inductive effects