o chem– fundamentals + isomerism + alkanes
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what is the empirical formula? (e.g. C3H6 => CH2)
it is the simplest formula that shows the ratio of all the different atoms in a molecule
what is the molecular formula?
it is the actual number of atoms of each element in a molecule
why is the structural formula useful?
it clearly shows how the atoms are bonded to each other
give me two types of aliphatic (open chains) hydrocarbons
• straight-chain • branched
what class of compounds has the structure –C☰C–
alkyne
what structure do arenes have?
benzene ring
what structure do ethers have
R–O–R
what’s the structural difference between ketones and aldehydes?
• ketone structure is R–C–H 〢 O • aldehyde structure is R–C–R 〢 O
is this an amide or an amine: –NH2
amine
what class of compounds is this structure?R–C–NR2 〢 O
amide
what defines a homologous series?
• same functional group • each successive member increases by one –CH2 unit
homologous series have the following characteristics: - same _______ formula - show a gradual change in _______ properties as molar mass increases - have similar ________ properties
general, physical, chemical
why is there resonance in benzene?
benzene has a delocalised π electron system
benzene is stable because…
it is resonance stabilised
what hybridisation does C in benzene undergo
sp2
why is benzene so stable? (4)
• each C atom is sp2 hybridised • each C atom contains one unhybridised p orbital that lies perpendicular to the plane of the benzene ring • the p orbitals overlap sideways with one another -> continuous overlap of unhybridised p orbitals • π e- can delocalise across benzene ring -> creates delocalised π e- cloud -> resonance
what are the effects of resonance stability on benzene 1. ??? 2. planar molecule 3. can undergo substitution rxns
identical C-C bond lengths
why does benzene have identical C-C bond lengths?
• due to the partial double bond character of C–C bonds • as a result of delocalisation of π e- across the ring
why does benzene undergo substitution but not addition rxns?
• sub rxns preserve the resonance stability of benzene • add rxns disrupt resonance stability -> energetically unfavourable
what are the two reactions benzene can undergo?
• nitration • reduction
chain isomers have the same ______ formula and functional group, but different ________ skeleton
molecular, carbon
positional isomers have different positions of ______________
functional group
aldehydes are functional grp isomers with …
ketones
carboxylic acids are functional grp isomers with…
esters