aromatic compounds, carbonyl and amines Flashcards
(60 cards)
What is the molecular formula of benzene
C6H6
What are aromatic, aliphatic and alicyclic compounds
Aromatic- containing benzene
aliphatic- ogranaic compound with open chain structure, can be cyclic but not benzene
alicyclic- cyclical but not benzene
What was kekule model for benzene
6 member ring of carbon with alternating single and double bonds, snake eating tail
Why did chemists disapprove with the kekule model
The model contain explain the physical and chemical properties of benzene
What are the factors that disprove the kekule model
1- benzene contains double bonds and therefore should decolourise bromine what but instead it doesn’t undergo any electrophillic addition reaction(therefore cannot have C=C) bonds
2- The bond length measure using X-ray diffraction showed that the bond length of each C bond was the same meaning that there were no double bonds
3- due to the double bonds the enthalpy of hydrogenation was expected to be *3 that of cyclohexene but it is actually much lower -208 so benzene is more stable
Delocalised model of benzene
- Each carbon atom has an electron in a p-orbital at right angles to the plain of bonded H atoms causing adjacent P orbitals to overlap causing a ring with high electron density
-Pi bond system spreads over all the carbon atoms, they are said to be delocalised
What are the groups that are prefixes to benzene
short alkyl chains, halogens and nitro groups
What happens when the carbon chain is longer than 7
the benzene is considered substituent and becomes the prefix eg phenyl ethanone
What are the 3 expections to this
Benzoic acid, phenylamine, benzaldehyde
What kind of reaction does benzene undergo
Electrophillic substitution, electrophile attracted to high electron density(strong electrophiles)
How do substitution reactions work on benzene
Hydrogen atom on benzene is replaced by atom atom/ group
conditions for nitration of benzene
catalysed by sulfuric acid and heated at 50 degrees
Conditions of acylation of benzene
60 degrees with halogen carrier
conditions for halogenation of benzene
Room temperature with halogen catalyst
Condition for alkylation of benzene
Room temperature with halogen carrier
catalyst for the Nitration of benzene
HNO3
creation:
HNO3 + H2SO4 -> HSO4 + H2NO3
H2NO3 -> NO3- + H2O
restoring catalyst
HSO4- + H+ -> H2S04
Halogen carrier for alkylation of benzene
Creation
CH3Cl + AlCl3 -> CH3+ + AlCl4-
AlCl4- + H+ -> AlCl3 + HCLl
Halogen carrier for acylation of benzene
Ch3COCl + AlCal3 -> Ch3CO+ + AlCl4-
All the hydrogen carriers
AlCl3, AlBr3, FeCl3
Why does benzene require halogen carriers
Too stable to react with non-polar or weak electrophiles to electrophiles produced from halogen carrier catalysts are much stronger
What is an electrophile/ nucleophile
electrophile- Chemical species that forms bonds by accepting a pair of electrons
nucleophile- Chemical species that form bonds by donating a pair of electrons
Comparing alkene to reactivity of alkenes
- Pi bond in alkenes are localised above and below the 2 carbons in a double bond for an area of high electron density
- These electrons induce a dipole in the non polar bromine making one of them slightly positive
- slightly positive bromine enables bromine to act as an electrophile
Comparing alkenes and benzene
- Benzene doesn’t react with bromine unless it has a halogen carrier, due to delocalised pi electrons above and below the Carbon ring
What is phenol
Benzene ring with an OH group(c6h5OH)
