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Starter A dye can be made from 4-methylphenylamine and 2,6-dimethylphenol, shown below OH H3C H3C CH3 NH2 4-methylphenylamine 2,6-dimethylphenol 1)Identify the inorganic nitrogen-containing compound formed by the mixture of hydrochloric acid and sodium nitrite. 2) Draw the structure of the organic compound formed in the ice-cold acidic mixture, showing a displayed formula of the nitrogen-containing group. 3)Suggest the structure of the dye. Amino acid L.O.: • State the general formula for an α-amino acid as RCH(NH2)COOH. • State that an amino acid exists as a zwitterion at a pH value called the isoelectric point. • State that different R– groups in α-amino acids may result in different isoelectric points. • Describe the acid–base properties of α-amino acids at different pH values. General formula of an α-amino acid Structures of some amino acids The R group There are 20 different amino acids The only difference is the atoms making up the R group The simplest R group is found in glycine where R = H The largest R group is in tryptophan Where is the alpha carbon in this amino acid? AMINO ACIDS H H2N amine group C R COOH carboxylic acid group H H2N C COOH H glycine H H2N C COOH CH3 alanine H H2N C CH COOH CH3 CH3 valine H H2N C COOH CH2OH serine H H2N C COOH CH2COOH aspartic acid • amino acids are chiral (except glycine where R = H) • only one enantiomer occurs usually Formation of a zwitterion from glycine © Pearson Education Ltd 2009 This document may have been altered from the original A zwitterion is a dipolar ionic form of an amino acid that is formed by the donation of a hydrogen ion from the carboxyl group to the amino group. The isoelectric point is the pH value at which the amino acid exists as a zwitter ion. Acid–base reactions of an amino acid Draw the structure of the amino acid at the pH shown. pH 12 pH 2 H H2N C H H2N COOH pH 13 H H2N C COOH H CH3 pH 4 C H COOH CH2OH H2N C COOH CH2COOH Draw the structure of the amino acid at the pH shown. pH 12 pH 2 H H2N C _ COO H + H3N C COOH H CH3 pH 13 pH 4 H + H3N C H COOH CH2OH H2N _ C COO _ CH2COO Isoelectric Points A Question: If glutamic acid, HOOCCH2CH2CH(NH2)COOH has its isoelectric point at pH 3.22, what will its structure be at: a) pH 3.22? b) pH 1? c) pH 13?
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