Module 6 Benzene and other arenes

what are sigma bonds

strong bonds with 2 s orbitals overlapping

what are pi bonds

weaker bonds with 2 p orbitals overlapping

what does the ring on benzene signify

delocalised pi bonds above and below

what shape is benzene

planar (flat), a regular hexagon shape

what bond angles does benzene have

120 degrees

what do benzenes carbons make

each make 3 bonds

what happens to benzene in bromine water

does not decolourise (stays orange)

what are the 4 ways to tell you the root name is benzene

an alkyl group up to 7 carbons long (e.g. methyl ethyl), a halogen (bromo chloro fluoro), a nitro group (NO2), a carboxylic acid (COOH)

what is this

methylbenzene

what is this

nitrobenzene

what is this

chlorobenzene

what is this

benzene carboxylic acid

what is this

1,3-dimethylbenzene

what is this

1,3-dinitrobenzene

when is the root name phenol

with most other functional groups or attached to chain with 7 or more carbon atoms

what is this

phenylamine

what is this

phenylethene

what is this

phenylethanone

what is this

butylbenzene (carbon one of the butyl group is attached to the benzene)

what is this

2-phenylbutane

what is this

phenyltmethanal

what is this

phenylethanoate (the benzene is on the -O section of the ester functional group so comes first in the name as a phenyl group)

what colour is benzene

colourless

what smell is benzene

sweet smelling

how flammable is benzene

highly flammable liquid

where is benzene found

found naturally in crude oil, component of petrol, found in cigarette smoke

what is benzene classified as

a carcinogen, can cause cancer

how reactive is benzene

unreactive

what are the derivatives of benzene

many aromatic compounds can be synthesised from benzene

what is the kekule model

structure of benzene based on 6 membered ring of carbon joined by alternate single and double bonds

why is the kekule model disaproved

not able to explain all its chemical and physical properties, lack of reactivity of benzene, length of C-C bonds, hydrogenation enthalpies

why does the lack of reactivity in benzene disapprove the kekule model

if it contained c=c bonds it should decolourise in brome in an electrophilic addition but it doesnt undergo electrophilic addition reaction and does not decolourise under normal conditions

why do the lengths of C-C bonds in benzene disapprove the kekule model

use xray diffraction to measure bond lengths in a molecule, single bond is 0.153nm and double bond is 0.134nm but bonds in benzene are 0-139nm,

why do hydrogenation enthalpies in benzene disapprove the kekule model

if benzene had kelule structure then it would have hydrogenation enthalpy 3x of cyclohexa-1,2,5-triene (kekule structure name) which is -120KJmol-1 so would be -360 but is -208

where in each carbon atoms of benzene are the electrons

1 electron is in p orbital at right angles to plane of bonded carbon and hydrogen atom

where do the p orbital electrons overlap in benzene

adjacent p orbital electrons overlap sideways above and below plane of carbon atoms to form ring of electron density

what do the overlapping p orbitals create in benzene

pi bonds which spread all over 6 carbon atoms in ring structure (the 6 electrons are delocalised)

what ones do i need to remember

benzoic acid (benzenecarboxylic acid), phenylamine, benzaldehyde (benzenecarbaldehyde)

what happens to compounds with more than 1 substituent group

ring is numbered just like a carbon chain starting in alphabetical order using smallest numbers possible