Benzene

methyl benzene hydrogenated 3 times creates

2-methyl-1,3,5-trinitrobenzene Trinitrotoluene - TNT

Describe the shape of, and bonding in, a molecule of benzene

6 C atoms in a hexagonal ring, with one H atom bonded to each C atom. Each C atom is bonded to two other C atoms and one H atom by single covalent σ-bonds. The angle between all the bonds is 120°. The 4th C electron is delocalised: all 6 spare p-orbitals overlap and the 6 electrons move freely within the overlapping orbitals. This leaves one unused electron on each C atom in a p orbital, perpendicular to the plane of the ring. The Six p electrons are delocalised in a ring structure above and below the plane of carbon atoms. The six electrons in the pi bonds are delocalised and spread out over the whole ring. Delocalised means not attached to a particular atom.

Equation for formation of the electrophile in Friedel Crafts

AlCl₃ + CH₃COCl → CH₃CO⁺ + AlCl₄-

Why is benzene enthalpy lower than cyclohexatriene

Benzene is more stable than cyclohexatriene. Expected hydrogenation of C6H6 is -360 kJ mol⁻¹ but actual is 152 kJ mol-1 (less exothermic) due to delocalisation of electrons

Friedel Crafts Acylation change in f.g.

Benzene→phenyl ketone Important in organic synthesis because introduces a reactive fg on to the benzene ring

Length and strength of benzene bonds

Bond length and energy between reg length of single and double (sing longer). All the C-C bonds are the exactly same length if weren't shape would be strained.

acylium ion formation

CH₃COCl + AlCl₃ → CH₃CO⁺ + AlCl₄⁻

Conditions and reagents for nitration of benzene

Conc nitric acid in the presence of conc sulphuric acid (catalyst) 50°C if using higher temps a second nitro group can be substituted.

Uses of phenyl amine

Dye, manufacturing polyurethane

What gas is given off in freidel crafts acylation

HCl, see misty white fumes

Equation for formation of nitronium ion

HNO₃ + 2H₂SO₄ → NO₂⁺ + 2HSO₄⁻ + H₃O⁺

Which is more stable cyclohexa-1,3-diene or cyclohexa-1,4-diene?

In cyclohexa-1,3-diene, there would be some delocalisation and extra stability as the pi electrons are close together and so overlap. The hydrogenation value would be less negative than -240 kJ/mol (showing more stable). In cyclohexa-1,4-diene, there would not be delocalisation as the pi electrons are too far apart and so don't overlap. The hydrogenation value would be -240 kJ/mol

Toxicity of Benzene

It is a carcinogen (cancer causing molecule) and is banned for use in schools. Methylbenzene is less toxic and also reacts more readily than benzene as the methyl side group releases electrons into the delocalised system making it more attractive to electrophiles.

Reactions of Benzene

Most of Benzene's reactions involve substituting one H for another atom or group of atoms. Benzene has a high electron density and so attracts electrophiles. It reactions are usually electrophilic substitutions.

Products of benzene with nitric acid in the presence of sulphuric acid

Nitrobenzene

Is benzene reactive?

No electrons in an energy potential well. Have v low energy hard to move to place w lower e as lower e than when confined to orbital.

What are aliphatic organic chemicals?

Organic substances with a straight or branched chain

What are aromatic or arene organic chemicals?

Organic substances with one or more ring(s) of 6 carbon atoms with delocalised bonding.

Products of nitrobenzene with tin and concentrated hydrochloric acid

Phenylamine

Products of benzene with propanoyl chloride in the presence of aluminium chloride

Phenylpropanone

Friedel Crafts Acylation reagents and conditions

Reagents: acyl chloride (CH₃CO⁺) in the presence of anhydrous aluminium chloride catalyst NB Electrophile can be any acyl chloride RCOCl The electrophile is the RCO+. Conditions: heat under reflux (50°C)

Reduction of nitrobenzene

Sn and conc HCl Use [H] to show red agent, forms water and phenyl amine

Explain why benzene does not readily undergo addition reactions

The delocalised electrons give stability to the benzene molecule that normal "double bonds" do not. Addition reactions break the delocalised ring, so are not favoured.

Explain why phenylamine is a weaker base than ethylamine

The lone pair on the N is drawn into the delocalised system so is less available for bonding with a proton

Equation for nitration of methyl benzene

methyl benzene + HNO₃ → nitromethyl benzene + H₂O