✅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
What are the inorganic products in alkylation?
HCl and AlCl3
What are the organic products in acylation?
HCl and AlCl3
What does Friedel-Crafts Acylation produce?
Phenylketones
What is benzene refluxed with in acylation?
An acyl chloride
What must the temperature be kept below for nitration of benzene?
55 degrees C
What happens if the temperature is above 55 for nitration of benzene?
Multiple substitutions occur
Why is phenol more reactive than benzene
The OH group makes it more likely to undergo electrophillic substitution
One of the lone pairs in oxygen p orbital becomes delocalised, increasing electron density of the ring
What happens if you shake phenol with bromine water?
It decolourises it
Why does substitution occur more than once on phenol?
The OH group makes it very attractive to electrophiles
What can aspirin be synthesised from?
Salicylic acid and ethanoic anhydride
What is the amine functional group?
-NR2, where R is an alkyl group or hydrogen
What can aliphatic amines be made from?
Halogenoalkanes or nitriles
What are amines?
Weak bases, as they accept protons
What does the strength of the amine base depend on?
How available the nitrogen’s lone pair of electrons is
What is the order of basicity?
Primary aromatic amine < Ammonia < Primary aliphatic amine
Why are the aliphatic amines the strongest bases?
The distribution of negative charge is distributed entirely on the lone pair, whereas in the aromatic amine it is distributed widely
What are small amines soluble in?
Water, as the amine group can form hydrogen bonds with the water molecule
The bigger the amine the greater the…
…London forces
What kind of solutions do amines form?
Alkaline
What do amines form with Copper (II) ions?
Complex ions
What complexes do Cu2+ ions form with water?
[Cu(H2O)6]2+ - a blue solution
What complex is formed if a small amount of butylamine solution is added?
[Cu(OH)2(H2O)4] - a blue precipitate
If more butylamine solution is added, how does the complex change?
[Cu(CH3(CH2)3NH2)4(H2O)2]2+ - a deep blue solution
How do amines react with halogenoalkanes?
In nucleophillic substitution reactions
How can N-Substituted Amides be made from amines?
By acetylation
Amides are…
…carboxylic acid derivatives
What is the amide functional group?
-CONH2
Why do amides behave differently from amines?
Because the carbonyl group pulls electrons away from the rest of the group
What suffix do amides have?
-amide
What can amides be made from?
Acyl chlorides
What are the reactants needed to make a primary amide?
An acyl chloride and concentrated ammonia
What reactants are needed to make an N-substituted amide?
An acyl chloride and primary amine
What is an N-substituted amide?
One of the hydrogens in NH2 is substituted with an alkyl group
What are amide links?
-CONH-
What reacts to form an amide link?
-COOH and -NH2
Which two types of molecule form a polyamide?
Dicarboxylic acids and diamines
What are proteins?
Condensation polymers of amino acids
What is needed to hydrolyse a protein into amino acids?
6moldm-3 hydrochloric acid and reflux
Which two types of molecule form a polyester?
Dicarboxylic acids and diols
What is an ester link?
-COO-
What functional groups do amino acids have?
NH2 and COOH
What is a zwitterion?
An overall neutral molecule that has a positivie and negative charge on different parts of the molecule
In acidic conditions, which part of the amino acid is changed?
The NH2 becomes protonated, forming NH3+
What charges does the amino acid have at its isoelectric point?
The NH2 becomes NH3+ and the COOH becomes COO-
In alkaline conditions, which part of the amino acid is changed?
The COOH group becomes COO-
Most amino acids are…
…chiral
What can be used to identify unknown amino acids?
Paper chromatography
How would you calculate an Rf value?
Distance travelled by spot/distance travelled by solvent
What is the general formula of a Gringard reagent?
RMgX
How are Gringards reagents made?
By refluxing a halogenoalkane with magnesium in dry ether
What would a Gringard’s reagent + CO2 form?
A carboxylic acid
What are the conditions needed to form a carboxylic acid from Gringards and CO2?
Dry ether and dilute HCl
What do Gringards form in reaction with aldehydes and ketones?
Alcohols
What are the conditions needed to form an alcohol from Gringards + carbonyl?
Dry ether and dilute HCl
