Aromatics and amines

Describe the type of molecule benzene is and it's structure
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Describe the type of molecule benzene is and it's structure
A cyclic planar molecule
Has delocalised electron ring in centre high electron density
Causes all C-C bonds to be same length
Describe the Kekule model of benzene
- thought benzene was a planar, cyclic structure with alternating double and single bonds
- each carbon atom was bonded to one hydrogen
- he thought that the benzene was constantly flipping between the two isomers
Explain how to prove there is a delocalised system in benzene and not alternating double bonds
measure benzene's stability by comparing the change in enthalpy of hydrogenation in benzene vs cyclohexane, 1,3,5, triene
Theoretically, cyclic structure with ONE double bond has change in enthalpy of hydrogenation of -120kJ/mol
So, three bonds should be -120 x 3 = -360 kJ/mol
But...
Experimental value when found of benzene = -208kJ/mol
So more energy is needed to break bonds in benzene as deltaH is less exothermic so more energy is required
What are arenes?
Aromatic hydrocarbons containing one or more benzene rings.
What is a benzene with an OH group called
Phenol
What is a benzene with an amine group called (NH2)
Phenylamine
What is the mechanism arenes undergo and why
Electrophillic substitution as they have a high density of electrons in delocalised ring attracts electrophiles
Why can't arenes/benzene undergo addition reactions
Because it would disrupt the stability of the electron ring
Name the two types of reactions arenes undergo and what are their products generally used for
Friedal-Crafts acylation - pharmaceuticals
Nitration reaction - dyes for clothes/explosives
Describe the process of friedalcrafts acylation and what must be done first in order to carry it out
An acylation group (RCO-) is added to benzene to make it easier to modify
But first prepare a carbocation (very strong +be charge to attach the delocalised ring)
Prepare using AlCl3 (a halogen carrier) as a catalyst to produce a stronger electrophile
What do the first steps of friedalcrafts acylation look like as diagramsAlCl3 used as a hydrogen carrier and catalyst so will be restored completely at the end once carbocation is usedAfter formation of carbocation in friedalcrafts acylation what happensProcess is carried out under reflux as substances are volatile and don't want them to evaporate out with a dry ether solvent Delocalised electrons are attracted to carbocation charge AlCl4- forms bind with H+ forming Hcl and reforming AlCl3 Acyl group now attached to benzeneWhat are the start products heated first in the process of nitration and what are they heated with and what is formedConc HNO3 (nitric acid) + H2SO4 (sulfuric acid) heated with benzene forming (H2NO3+) nitrobenzene and (HSO4-)What is the next step in nitration reaction after nitrobenzene is formed (H2NO3+) and what is the product used forH2NO3+ decomposes to form the electrophile needed (NO2+) and water ——> NO2+ + H2O Electrophile used in electrophillic substitution of benzeneWhat does the mechanism of the electrophile produced in the nitration reaction reacting with benzene look like and what are the conditions necessaryKeep heat below 55 degrees to avoid multiple substitutionsWhat are aminesOrganic compounds derived from ammonia where a H is replaced by an alkyl groupWhat is a benzene with an amine group attached named as and what level of amine is it (eg primary secondary tertiary etc)Phenylamine PrimaryWhat are aliphatic aminesAmines without a benzene ringWhat are cationic surfactants and where are they usedQuaternary ammonium salts Used in cleaning products eg shampoosDescribe the structure of a quaternary ammonium salt eg terramethylamine Describe how they cause emulsionsPositive charged heads Non polar no charge long hydrocarbon tail Polar heads attracted to water tails attracted to non polar substance causing emulsionList the order of base strength with amines from weakest to strongest and explain whyAromatic amine —> ammonia —> primary amine Aromatic weakest as delocalised ring is electron withdrawing pulling the electron pair towards it so not as easy to be lost Primary/secondary/tertiary amines have alkyl groups that are electron pushing towards N so line pair more readily availableWhat are the two ways of making aliphatic aminesReacting a halogenoalkane + excess ammonia Or Reduction of nitrilesDescribe the process of making aliphatic amines when reacting "halogenoalkanes with excess ammonia" mechanism used and why it's not an ideal method of primary amines are only wantedNucleophillic substitution where ammonia acts as a nucleophile Then ammonia acts as a base (proton acceptor) Product and start reactant keep reacting as there's a line pair on N Don't get a good yield of primary aminesWhat are the two methods used when reducing nitriles and the reagents used1) Nickel catalyst + hydrogen gas , catalytic hydrogenation , cheapest 2) LiAlH4 + dilute HCl , reduction using strong reducing agent , expensive not used in industryWhat does the reaction of nickel and hydrogen gas in the reduction of nitriles look like and it's conditionsHigh temperature and pressureWhat does the reaction using strong reducing agents in the reduction of nitriles look like and it's conditionsLiAlH4 used dissolved in dry ether And dilute hydrochloric acidHow are aromatic amines produced? What are the conditions necessaryBy reducing a nitro compound eg nitrobenzene 1) heat nitrobenzene under reflux with conc HCl + tin catalyst forms salt 2) salt produced is reacted with an alkali (NaOH) producing aromatic amineWhat are amides and N substituted amidesCarboxylic acid derivatives where -OH is replaced with an amino group N substituted as the same but a hydrogen in amino group is replaced by an R group (alkyl group)