α-Amino acid, zwitter ion and amphoteric behaviourα-ऐमीनो अम्ल, उभयाविष्ट आयन और उभयधर्मी व्यवहारα-Amino acid, zwitter ion and amphoteric behaviour
NCERT 10.2.1–10.2.2 · Class 12 Chemistry · Chapter 10 · interactive diagram
Parts and what they mean
- General formula of an α-amino acid (α-ऐमीनो अम्ल का सामान्य सूत्र) — –NH₂ and –COOH on the same (α) carbon. Only α-amino acids are obtained on hydrolysis of proteins.
- α-Carbon (α-कार्बन) — Carries H, R, –NH₂ and –COOH. Asymmetric in every common amino acid except glycine (R = H), so they are optically active; most natural ones are L.
- R = side chain (R = पार्श्व श्रृंखला) — Different for each amino acid: glycine –H, alanine –CH₃, valine –CH(CH₃)₂, etc. (NCERT Table 10.2).
- Amino group (–NH₂), basic (ऐमीनो समूह (–NH₂), क्षारीय) — Can accept a proton. In an L-amino acid (Fischer projection, –COOH up) the –NH₂ is written on the left.
- Carboxyl group (–COOH), acidic (कार्बॉक्सिल समूह (–COOH), अम्लीय) — Can lose a proton.
- Amino acid written in the un-ionised form (अनआयनित रूप में लिखा ऐमीनो अम्ल) — The usual way of writing it, but in water and in crystals it exists mostly as the zwitter ion.
- Zwitter ion (उभयाविष्ट आयन (ज़्विटर आयन)) — Dipolar ion: neutral overall but has both + and − charges. Explains why amino acids are colourless, crystalline, water-soluble, high-melting solids that behave like salts.
- Internal proton transfer (आंतरिक प्रोटॉन स्थानांतरण) — The acidic –COOH loses a proton and the basic –NH₂ accepts it.
- With acid: zwitter ion acts as a base (अम्ल के साथ: उभयाविष्ट आयन क्षार की तरह) — –COO⁻ accepts H⁺ → cation ⁺H₃N–CHR–COOH.
- With base: zwitter ion acts as an acid (क्षार के साथ: उभयाविष्ट आयन अम्ल की तरह) — –NH₃⁺ gives H⁺ to OH⁻ → anion H₂N–CHR–COO⁻ + H₂O. Reacting with both acids and bases = amphoteric.
Original diagram drawn by Simple Learning Hub, based on NCERT 10.2.1–10.2.2. Report a mistake