Carbo Acids & Its Derivatives

Question 1

Factors affecting acidity of carboxylic acids.

Answer 1

• The electron withdrawing grp attached to the OH bond weakens it by withdrawing electrons,enhancing the loss of H (as a proton), hence enhances acidity.
• The negative charge on the carboxylate ion is spread all over the ion, thus stabilizing it & making the combin. with H less likely.
• The group attached to the carboxylic acid group ( if it is e withdrawing, easier for H to be lost. If e pushing, it neutralizes the electron pull of the carbonyl).

Question 2

About Methanoic acid.

Answer 2

• It is the strongest unsubstituted carbo.acid.
• It is oxidised by mild ox.agents to form CO₂ + H₂O
• Gives positive test with Fehling sol.(Cu² reduced to Cu¹, orange deposits seen) & Tollens reagent (Ag¹ reduced to Ag , silver mirror seen).
• It will change color of both KMnO₄ & K₂Cr₂O₇.

Question 3

Reaction of Ethanedioic acid .

Answer 3

The Mn(2 plus) ion produced serves as a catalyst. Therefore this is an example of auto catalysis.

Question 4

Preparing Acyl Chlorides. E.g=> PCl₅

Answer 4

• R.t.p/ no heating
• products-> Acyl chloride, POCl₃, HCl.
• Reagents-> carbo.acid and PCl₅

Question 5

Preparing Acyl Chlorides E.g => PCl₃

Answer 5

• Requires heating, No catalyst.
• Products-> Acyl chloride & H₃PO₃.
• same reagent as all other preparations.

Question 6

Preparing Acyl chlorides. E.g => SOCl₂

Answer 6

• R.t.p
• Products -> SO₂ & HCl
• Same reagents as other preparations.

Question 7

How does converting carbo.acids to acyl chlorides increase its reactivity?

Answer 7

The O of the carbonyl group, as well as the Cl atom will draw electrons strongly from the C atom, making it electron deficient . Hence the carbonyl carbon has a partial positive charge and increased likelihood of neuclophilic attack.

Question 8

Equation for the general reaction of Acyl chlorides.

Answer 8

ROCL + HZ —–> ROZ + HCl.

HZ -> e.g are: H₂O , ROH, NH₃, RNH₂ cuz of the lone pair of electrons on the oxygen and nitrogen.
R is the alkyl or aryl.
HZ is group acting as neuclophile.

Question 9

Why are reactions of acyl chlorides faster than that of chloroalkanes?

Answer 9

Cuz of the presence of the carbonyl group making it more open to neuclophilic attack.

Question 10

Why don’t aryl chlorides undergo hydrolysis?

Answer 10

Cuz the carbon carrying the halogen is part of the delocalised pi bonding system of the benzene ring. Causing the C-Cl bond to have some double bond character.

Question 11

Reaction of alcohol and phenol with acyl chlorides to produce esters and HCl , this reaction is much faster than the reaction of alcohol or phenol with carbo.acids.

Answer 11

Because of the carbonyl group making it more open to neuclophilic attack.

Question 12

Why can amines (RNH₂) act as Lewis bases?

Answer 12

Cuz they have a lone pair of electrons on the nitrogen. The nitrogen donates it’s lone pair of electrons to a proton to form a dative bond.

Question 13

When reacting HCl with ammonia or an amine …. How will the product look?

Answer 13

Add one H to the ammonia or amine making it a + ion and a Cl ion right beside it being a - ion.

Question 14

The strength of a base is based on ?

Answer 14

The ease or difficulty of loosing the lone pair of electrons on the nitrogen.

Question 15

Making amines:

Halo.alkane + excess ethanolic ammonia.

Answer 15

• Conditions-> Heat
• Reagents-> Halo.alkanes & excess eth. amm.
• Reason for excess-> prevents formation of secondary & tertiary amines and formation of amm. salts.

Question 16

Making Amines:

Halo.alkanes + cyanide ion.

Answer 16

• Conditions : Heat , reflux.
• Reagents: Halo.alkane one carbon short of goal & KCN in ethanol.
• The reaction forms a nitrile that can be further oxidised to form an amine.
• Reducing agents: LiAlH₄,NaBH₄, Nickel , H gas.
• Amides can also form amines using LiAlH to reduce it.

Question 17

Making phenyl amine.

Answer 17

• Made by reducing Nitrobenzene.
• Reagent : Tin in HCl & Nitrobenzene.
• steam distillation is used to get it from the mixture.

Question 18

Phenyl amine reacts with aq bromine in a similar way to phenol and?

Answer 18

aq bromine.

Question 19

Diazotisation process. ( formation of azodyes)

Answer 19

• Phenylamine reacts with HNO₂ to produce diazonium salt.
• HNO₂ is unstable so it is made in situ by reacting sodium nitrate with dilute HCl.
• Conditions: reactn. mix must be kept below 10⁰C using ice as the diazonium salt is unstable & decomposes easily giving N gas.
• The ion reacts with an alk. sol. of phenol (coupling).
• The reactn. prod. vry stable azodye (it is orange) cuz the delocalised pi bonding system between 2 benzene rings is extended through the N=N group which acts as a bridge.
• The azo is formed immediately.

Question 20

Amino acids have 2 func.groups, namely…..

Answer 20

Carbo. acids & Amines.

Question 21

How is a Zwitterion ion formed ?

Answer 21

By reaction between the -COOH & -NH₂ of the same amino acid. ( the latter gains one H and the former loses its H).

Question 22

Consequences of the Zwitterion ion.

Answer 22

• Amino acids have relatively strong intermolecular forces of attraction (due to ionic nature) hence they’re crystalline solids and are soluble in water.
• Solution of amino acids act as a buffer (resists PH changes).

Question 23

How is an Amide formed?

Answer 23

From the reaction between a carbo.acid functional group and amine functional group.
(It means amino acids can form Amide linkages and peptide linkages).

Question 24

Difference between amides and amines. (In terms of PH).

Answer 24

Amines are basic, while amides are neutral.

Question 25

Why are amides neutral?

Answer 25

Cuz the lone pair on the nitrogen atom is made unavailable due to the electron withdrawing effect of the carbonyl oxygen.

Question 26

Formula for making amides.

Answer 26

(Acyl Chloride)RCOCl + R¹-NH₂ —-> RCONHR¹ + HCl.

Question 27

If amine is in excess during the formation of amide, then?

Answer 27

The inreacted amine can react with the HCl to form a salt.

Question 28

In naming amides, when N precedes the name of the amide (e.g N,N-diethylbutane amide), it means 1 H has been replaced by an alkyl group on the amine part of the molecule.

Answer 28

Just for reading.

Question 29

For hydrolysis of amides.

Answer 29

(R-CO-NHR¹)
•The C-N bond is broken and OH is added, except in alkali hydrolysis where Na can still react with OH.
•Conditions-> Reflux with acid or alkali.

Question 30

Explain electrophoresis.

Answer 30

It is like chromatography.
•It involves separating ions in an electric field.
•Ions will migrate on the principle of opposites attract.
•It is commonly used to separate, identify or purify proteins.

Question 31

Describe the electrophoresis set up.

Answer 31

• The sample is placed on an absorbent paper or gel.
• The ions are separated by a buffer solution & move along the paper or gel.
• The rate of movmnt. of the ions are dependent on several factors, including: ion size and charge.
• The product (electropherogram) consists of a series of lines or bands, indicating the diff. components of the mixture.

Question 32

If the bands of an electropherogram are not visible……

Answer 32

you can use UV light or chemicals to make it visible.

Question 33

Why is a buffer used in electrophoresis?

Answer 33

Cuz the charge on an amino acid is PH dependent. Therefore pH will affect movement of ions.