Chemistry Unit 5 flashcards: arenes, benzene

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A2 level Chemistry (Unit 5) Flashcards on Chemistry Unit 5 flashcards: arenes, benzene, created by J000D97 on 04/05/2015.

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Question Answer
Benzene properties Characteristic odour Immiscible in water \(C_6H_6\) colourless liquid High C:H ratio
2 pieces of evidence against the Kekule structure 1) Substitution and addition reactions do not occur easily like in alkenes. Thermochemical evidence H formation is less positive than expected suggesting it is more stable than the proposed structure.
What does the difference between enthalpy of hydrogenation of cyclohexene and benzene show? The energy taken in to overcome the stable benzene resonance structure.
What is the bond length in benzene? 0.139nm
Describe the arrangement of electrons in benzene Each C forms a sigma bond with adjacent C atoms forming a planar carbon hexagonal skeleton. Each C then has 1 p orbital containing 1 electron and the orbital lobes fuse to form 2 areas of delocalised electron density above and below the carbon skeleton.
What do you see when benzene is burnt in air? A smoky yellow flame
Benzene with bromine in UV is what type of reaction? Free-radical addition
What do halogen carrier catalysts do to \(Br_2\) molecules? Polarise it
Does benzene react with conc nitric acid on its own? No
Which is a stronger acid sulphuric or nitric? Sulphuric
Temperature conditions for nitration of benzene Below 55\(\omicron\)
Method for nitrating benzene Add benzene dropwise from a tap funnel to nitrating mixture in a cold flask.
What occurs when nitrating benzene if the temperature rises above 55? Multiple substitution
Properties of nitrobenzene Toxic Flammable Pale yellow Liquid Aromatic Odour of bitter almonds
What is fuming sulphuric acid? Conc. sulphuric with additional \(SO_3\)
Name of mechanism for and conditions of alkylation and acylation Electrophillic substitution Reflux
What type of reactions are acylation and alkylation called? Friedel Craft's reactions
Conditions for addition of \(H_2\) to benzene Raney Ni cat 150 degrees
Benzene activated and non-activated positions 2,4,6 = activated 1, 3, 5 = non-activated
Does OH activate the ring? Yes
What colour and state is 2, 4, 6 - tribromophenol? Solid white
Phenol reacts with dilute nitric acid? Yes
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