7.9.3  AMINO ACIDS

QUESTIONS

Section A

For each of the questions only one of the lettered responses (A – D) is correct.

 

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet.

 

1               Which one of the following reactions will glycine (2-aminoethanoic acid) not undergo?

 

A  H2NCH2COOH  +  HNO2                                   HOCH2COOH  +  H2O  +  N2

B  H2NCH2COOH  +  HCl                                      HOOCCH2NH3+Cl-

$C  H2NCH2COOH  +  H2                                        CH3COOH  +   NH3

D  H2NCH2COOH  +  NH3                         H2NCH2COO-NH4+

 

2       

 

 

Section B

Answer all questions in the spaces provided.

 

1.            “Diet” beverages are often sweetened by aspartame.

 

(a) (i)   When isolated and then hydrolysed, aspartame yields two organic products, one of which is alanine.

 

            Draw the structure of alanine.

                        CH3                                    or                        HOOC.CH(CH3)NH2

                        ç

          HOOC¾C¾NH2

ç

                        H

Error[-1] eg no H’s

           

                                                                                                                                   

                                                                                                                                    [2]

    (ii)    Alanine is optically active. Explain what is meant by this term.

Optically active: (A solution of) alanine turns/ rotates/ bends [1] the plane of polarised light [1]

Changes [-1]

 

                                                                                                                                   

 

                                                                                                                                   

 

                                                                                                                                   

 

                                                                                                                                   

                                                                                                                                    [2]

(b)        Describe what is observed and give balanced equations for the reactions of alanine with solutions of:

 

   (i)    sodium carbonate

 

bubbles (of carbon dioxide) evolved/ gas/ effervescence [1]

fumes [-1] each time

Na2CO3 + 2HOOCCH(CH3)NH2                        2Na+ -OOCCH(CH3)NH2 + H2O + CO2            [2]

 

-OOCCH(CH3)NH3+   CO2 and N2 produced º [1]

error [-1]            charges may be omitted

                                                                                                                                   

 

                                                                                                                                   

 

                                                                                                                                   

                                                                                                                                    [3]

(ii)               nitrous acid

 

bubbles (of nitrogen)  evolved/ gas/ effervescence [1]

HOOCCH(CH3)NH2 + HNO2     HOOCCH(CH3)OH + N2 + H2O  [2]

Error [-1]  wrong gas in either case [-1]  charges may be omitted

                                                                                                                                   

 

                                                                                                                                   

 

                                                                                                                                   

                                                                                                                                    [3]

(c)                Name the family of organic compounds to which alanine belongs.

 

Amino acids (not proteins)            [1]

                                                                                                                                   

[1]

                                                                                                            CHM3J8

 

2                    Nylon 6,6 has the formula

 

-(CH2)4-CONH-(CH2)6-NHCO-(CH2)4-CONH-(CH2)6-NHCO-

 

(a)                Give the formulae of the two monomers which combine to make nylon 6,6

 

ClOC(CH2)4COCl  [1] and H2N(CH3)6NH2 [1] or equivalent formula 

1                                                                                                                                  

                                                                                                                                    [1]

2                                                                                                                                 

                                                                                                                                    [1]

 

(b)               What is the name of the other product in this polymerisation.

 

Hydrogen chloride / H2O  [1]

                                                                                                                                   

[1]

 

(c)                Suggest, including an equation, what will happen if nylon 6,6 is boiled with dilute acid.

 

Hydrolysis will occur/ resulting in breaking of C-N bond/ peptide bond  [1]

Production of dicarboxylic acid and production of diamine/ monomers reformed (if acid quoted) (both needed)  [1]

-(CH2)4-CONH-(CH2)6-NHCO-(CH2)4-CONH-(CH2)6-NHCO- + H2O     

HOOC-(CH2)4-COOH  +   H2N-(CH2)6-NH2  [2]

2 errors [-1] or –CONH- + H2O     -COOH + H2N-  [1 only]

 

                                                                                                                                   

 

                                                                                                                                   

 

                                                                                                                                   

 

                                                                                                                                   

[4]

                                                                                                            CHM3J8

 

3              The dipeptide shown below may be obtained by hydrolysis of protein material.

 

                     H          O

                      ç       //    

H2N— C—  C               O

          ç      \             //      

         CH3     NHCH2C

                                 \       

                                  OH

 

(a)         What is the name given to the functional group inside the rectangle?

 

Peptide link / amide   [1]

                                                                                                                          

                                                                                                                                    [1]

 

(b)         Write an equation for the further hydrolysis of this dipeptide.

           H          O                O           O

                      ç       //                //        //

          H2O  +    H2N— C—  C               O       H2NC—C   +   H2NCH2C         [2]

          ç       \          //                    ç     \         \

         CH3     NHCH2C                CH3  OH        OH

              \       

               OH

Each error [-1]

If acid /alkali used formulae on RHS must be correct

 

                                                                                                                          

                                                                                                                                    [2]

                                                                                                                        CHM3F8