✅18 - Organic Chemistry III Flashcards
What are aromatic compounds?
Compounds containing a hydrocarbon ring containing delocalised electrons
What are aliphatic compounds?
Ones which do not have a hydrocarbon ring with delocatised electrons
What is benzene described as?
An arene
What are the physical properties of benzene?
A colourless liquid
Boiling temperature of 80 degrees
Insoluble in water
What is the molecular formula of benzene?
C6H6
What is the Kekule structure of benzene?
Alternating double and single bonds in a cyclic structure with a ring of hydrogen around it
How does bromine water disprove the Kekule structure?
If benzene contained three C=C bonds, it would readily decolourise bromine water, but it does not, suggesting there are no double bonds
How do the isomers of dibromobenzene disprove the Kekule structure?
If the Kekule structure is correct, there would be four isomers of dibromobenzene, however only three are known to exist as there are no C=C bonds
How do bond lengths disprove the Kekule structure?
C-C bonds and C=C bonds are different lengths, but in benzene the bonds lengths are all the same, so there cannot be different types of bonds in the molecule
How do enthalpy changes of hydrogenation disprove the Kekule structure?
The actual enthalpy change of hydrogenation of benzene differs from the theoretical value for if it had C=C double bonds
What are the four factors which disprove the Kekule structure?
Bromine water
Isomers of dibromobenzene
Bond lengths
Enthalpy change of hydrogenation
In the actual structure of benzene how are the electrons aranged?
In two delocalised rings, one above and one above the Carbon ring, of pi electrons
What are the conditions needed for hydrogenation of benzene?
Hydrogen, and heating under pressure with a nickel catalyst
What is the equation for the hydrogenation of benzene?
C6H6 + 3H2 ——> C6H12
What type of flame does benzene give?
A smoky flame
What are halogen carriers?
Usually metal-halogen compounds such as aluminium chloride
What are the products of bromination of benzene?
Bromobenzene and hydrogen bromide
What is nitration of benzene?
The substitution of a hydrogen atom by a nitro group, NO2
What are the conditions needed for nitration of benzene?
Warming it with a mixture of conc nitric acid and sulfuric acid catalyst
What are the products of nitration of benzene?
Nitrobenzene and water
What are two of the types of Friedel-Crafts reactions?
Alkylation and acylation
What are the features all Friedel-Crafts reactions have in common?
Using reagent XY, one of the hydrogens In benzene is substituted by Y, and the other product is HX
A catalyst is needed
Anyhydrous conditions are needed because water would react with catalyst and organic product
What is an alkyl group?
CH3
What is an acyl group?
COCH3
What is the reactant for alkylation of benzene?
A halogenalkane, such as CH3Cl
What are the products of alkylation of benzene?
An alkylbenzene such as methylbenzene and hydrogen chloride
What are the products of the acylation of benzene?
A ketone (phenylethanone) and hydrogen chloride
What name is often used when the benzene ring is attached of another functional group?
Phenyl or phen
What makes benzene act as an electrophile?
The delocalised electrons
How does Bromine react with the catalyst in Bromination of Benzene?
It forms Br+
What is the equation for the reaction between Bromine and the halogen carrier in Bromination?
AlCl3 + Br2 ——> Br+ + AlCl3Br-
What are the inorganic products formed in the bromination of benzene?
AlCl3 and HBr
What is the first step in Nitration of Benzene?
Formation of an electrophile through nitric acid and sulfuric acid reacting to form NO2+
What is the equation for the reaction to form an electrophile?
HNO3 + H2SO4 ——> NO2+ HSO4- +H2O
What type of mechanism is Alkylation of benzene?
Electrophillic substitution