Flashcards
3.6 Aromatic compounds and Amines
Cards in this deck (22)
- 1BenzeneC6H6 has a planar cyclic structure (6 carbon atoms in a flat ring). Each carbon atoms forms single covalent bonds to the carbons on either side and one to a hydrogen atom. The final unpaired electron is located in the p-orbital that sticks out above or below the plane of the ring-> ring of delocalised electrons.
All the c-c bonds are the same, same length (140pm) between a C-C single and C=C double bond. - 2description
- 3delocalised ring of electrons makes benzene stable
- 4aromatic compounds derive from benzene (arenes)...
- 5naming simple derivatives of benzene
- 6two or more substituents present
- 7substituent side group
- 8Arenes undergo electrophilic substitution reactionshigh electron density of benzene ring attracts electrophiles but as the ring is stable it doesn't undergo electrophilic addition, it undergoes substitution and one hydrogen is substituted.
- 9Friedel Crafts Acylation -add an acyl group (RCO-) to the benzene ringan electrophile has to have a strong positive charge to attack the benzene ring and as they are not polarised they are made into stronger electrophiles using a catalyst called a halogen carrier, AlCl3
acyl chloride= electrophile and AlCl3= halogen carrier - 10AlCl3 makes the acyl chloride electrophile stronger byaccepting the lone pair of electrons, polarising the acyl chloride to form a carbocation (strong electrophile)
- 11mechanism electrons in the benzene ring attracted to carbocation, electrons bond to carbocation- partially breaks delocalised ring and gives a positive charge negative AlCl4- ion is attracted to the positive ring and the chloride ion breaks away and bonds to the hydrogen, forming HCl and the reformed catalyst
- 12Nitration -warm the benzene ring with concentrated nitric and sulfuric acids to get nitrobenzene sulfuric acid acts as a catalyst helping make the nitronium ion, NO2+ which is an electrophile
- 13AminesOrganic Derivatives of Ammonia
If one hydrogen from NH3 is replaced with an organic group-> primary
2->secondary etc.
The lone pair of electrons on the nitrogen atom in a tertiary amine can bond with a fourth organic group giving a quaternary ammonium ion - 14quaternary ammonium saltscationic surfactants
positively charged so form quaternarary ammonium salts eg. tertramethylammonium chloride (CH3)4N+Cl-
salts with atleast one long chain are used in cationic surfactants. The hydrocarbon chain binds to nonpolar substances like grease whilt the cationic head dissolves in water and can bind to neg. charged surfaces such as hair getting rid of static (fabric conditioners, fabric cleaners, hair products)
- 15Amines have a lone pair of electrons so act asweak acids, accept protons- lone pair of electrons on nitrogen atom form dative covalent bond with H+ ion
The strength of the base depends on how available the nitrogen's lone pair of electrons is, the more available, the more likely to accept the proton and the stronger the base - 16A lone pair of electrons is more available if electron density is higherorder of base strength;
primary aromatic amine - 17lone pair of electrons means that amines are nucleophilesthey react with halogenoalkanes in a nucleophilic substitution reaction
react with acid anhydrides/chlorides in nucleophilic addition-elimination reactions - 18Aliphatic amines are made from either1. halogenolkanes
2. reducing nitriles - 19heat halogenoalkane with excess
- 20making amines by halogenoalkanes means you end up with a mixture of primary, secondary and tertiary amines and quat saltsbecause the primary amine has a lone pair of electrons-nucleophile. Further substitutions can take place
- 21Reducing nitriles into primary aminestwo methods;
1. lithium aluminium hydride in non-aqueous solvent followed by dilute ether
2. cheaper way is to reduce nitriles using hydrogen gas with a metal catalyst such as platinum or nickel at high temp and pressure (catalytic hydrogenation) - 22Aromatic Amines made byreducing a nitro compound
1. heat the nitro compound, tin metal and concentrated HCl under reflux to form a salt
2.turn the salt into an aromatic amine by adding an alkali such as NaOH solution
3.Aromatic amines can be used in organic synthesis for dyes and pharmaceuticals
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- A-Level Organic Chemistry Flashcards on 3.6 Aromatic compounds and Amines, created by nicola Goodship on 15/04/2017.
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