Alanine (ala, A) (neutral, non-polar) Arginine (arg, R) (basic, polar) Asparagine (asn, N) (neutral, polar) Aspartic Acid (asp, D) (acidic, polar) Cysteine (cys, C) (neutral, slightly polar) Glutamic Acid (glu, E) (acidic, polar) Glutamine (gln, Q) (neutral, polar) Glycine (gly, G) (neutral, non-polar) Histidine (his, H) (basic, polar) Isoleucine (ile, I) (neutral, non-polar) Leucine (leu, L) (neutral, non-polar) Lysine (lys, K) (basic, polar) Methionine (met, M) (neutral, non-polar) Phenylalanine (phe, F) (neutral, non-polar)

Proline (pro, P) (neutral, non-polar) Serine (ser, S) (neutral, polar) Threonine (thr, T) (neutral, polar) Tryptophan (trp, W) (neutral, slightly polar) Tyrosine (tyr, Y) (neutral, polar) Valine (val, V) (neutral, non-polar) Questions 1. ) Rank the following amino acids by increasing polarity. (i. e. 1 = more non-polar) ser ; glu ; asp ; lys ; ala ; gln 2. ) Which amino acid is most insoluble in water: isoleucine or alanine? 3. ) Which amino acid is most soluble in water: lys or ser? 4. ) Rank the following according to increasing non-polarity (i. e. = least non-polar, 4 = most non-polar) leu; phe; val; ala Answers 1. ) 1 = ala, 2 = lys, 3 = ser, 4 = glu, 5 = asp, 6 = gln 2. ) Isoleucine has more CH’s, therefore more insoluble than alanine 3. ) Ser because the alcohol group is more polar than the amine in lys 4. ) 1 = ala, 2 = val, 3 = leu, 4 = phe (ranking is based on ^ # of CH’s) Principles of Polarity * The greater the electronegativity difference between atoms in a bond, the more polar the bond. Partial negative charges are found on the most electronegative atoms, the others are partially positive.

In general, the presence of an oxygen is more polar than a nitrogen because oxygen is more electronegative than nitrogen. * The combination of carbons and hydrogens as in hydrocarbons or in the hydrocarbon portion of a molecule with a functional group is always NON-POLAR. Summary of Polarity Polarity ranking of the Functional Groups: (most polar first) Amide > Acid > Alcohol > Ketone ~ Aldehyde > Amine > Ester > Ether > Alkane An abbreviated list to know well is: Amide > Acid > Alcohol > Amine > Ether > Alkane

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