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Exercises · 16.27

Q.Label the hydrophilic and hydrophobic parts in the following compounds.

(i) CH3(CH2)10CH2OSO3⁻Na⁺
(ii) CH3(CH2)15N⁺(CH3)3Br⁻
(iii) CH3(CH2)16COO(CH2CH2O)nCH2CH2OH
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In each detergent molecule, the long non-polar hydrocarbon chain forms the hydrophobic part, while the charged or strongly polar terminal group forms the hydrophilic part.

(i) CH3(CH2)10CH2OSO3−Na+CH_3(CH_2)_{10}CH_2OSO_3^-Na^+ (an anionic/sulphate detergent)

  • Hydrophobic: CH3(CH2)10CH2−CH_3(CH_2)_{10}CH_2- (the C12 alkyl chain)
  • Hydrophilic: −OSO3−Na+-OSO_3^-Na^+ (the sulphate ester head group)

(ii) CH3(CH2)15N+(CH3)3Br−CH_3(CH_2)_{15}N^+(CH_3)_3Br^- (a cationic/quaternary-ammonium detergent)

  • Hydrophobic: CH3(CH2)15−CH_3(CH_2)_{15}- (the C16 alkyl chain)
  • Hydrophilic: −N+(CH3)3Br−-N^+(CH_3)_3Br^- (the quaternary ammonium head with its bromide counter-ion)

(iii) CH3(CH2)16COO(CH2CH2O)nCH2CH2OHCH_3(CH_2)_{16}COO(CH_2CH_2O)_nCH_2CH_2OH (a non-ionic detergent)

  • Hydrophobic: CH3(CH2)16−CH_3(CH_2)_{16}- (the C17 alkyl chain) …
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