OCR A Level Chemistry A: Amino acids, amides and chirality (H432) – Revision Notes

These notes condense section 6.2.2, Amino acids, amides and chirality, of the OCR A Level Chemistry A (H432) specification, Version 3.1 (May 2026), for first assessment in 2017. Full explanations sit in the study guide. The notes cover all four outcomes, 6.2.2(a) to (d), from Module 6, Organic chemistry and analysis, which the assessment overview places in components 02 and 03. H432 is the full A level, and no PAG is listed for this section.

Use the OCR chemistry hub for other topics and the printable checklist to record what is secure. Then try the practice questions, or try the free diagnostics for a course-wide check.

Outcome map

Outcome	One-line summary
6.2.2(a)	α-amino acid = RCH(NH₂)COOH; (i) COOH + alkali → salt, COOH + alcohol → ester; (ii) NH₂ + acid → ammonium salt
6.2.2(b)	Primary amide RCONH₂; secondary amide RCONHR′
6.2.2(c)	Optical isomers: non-superimposable mirror images about a chiral centre; draw them in 3-D (M4.2, M4.3, HSW1, HSW8)
6.2.2(d)	Find every chiral centre in any organic molecule (M4.2, M4.3)

Key definitions

• α-amino acid: NH₂ and COOH on the same carbon; general formula RCH(NH₂)COOH.
• α-carbon: the carbon carrying H, R, NH₂ and COOH.
• Primary amide: the amide nitrogen is bonded to one carbon (the C=O carbon), RCONH₂.
• Secondary amide: the amide nitrogen is bonded to two carbons, RCONHR′.
• Stereoisomers: same structural formula, different arrangement in space.
• Chiral centre: a carbon atom carrying four different atoms or groups.
• Optical isomers: a pair of non-superimposable mirror images about a chiral centre (enantiomers).

Amino acid reactions at a glance

Group	Reagent	Conditions	What forms	General equation
COOH	NaOH(aq) (any alkali)	room temperature	carboxylate salt + water	RCH(NH₂)COOH + NaOH → RCH(NH₂)COO⁻Na⁺ + H₂O
COOH	alcohol R′OH	concentrated H₂SO₄ catalyst, heat	ester + water (reversible)	RCH(NH₂)COOH + R′OH ⇌ RCH(NH₂)COOR′ + H₂O
NH₂	dilute HCl (any acid)	room temperature	ammonium salt	RCH(NH₂)COOH + HCl → RCH(NH₃⁺)COOH Cl⁻

Remember the pairing: alkali → COOH end, acid → NH₂ end, alcohol + acid catalyst → COOH end.

Method: writing any amino acid equation

1. Write the amino acid with R expanded, keeping NH₂ and COOH on the same carbon.
2. Decide which group the reagent attacks (table above).
3. Change only that group: COOH → COO⁻Na⁺, COOR′ or (for acid) NH₂ → NH₃⁺.
4. Add the by-product: H₂O for alkali and for esterification; nothing extra for HCl, but show Cl⁻.
5. Check atoms balance and that one mole of reagent reacts per group.

Worked reminder: alanine with sodium hydroxide

Alanine is CH₃CH(NH₂)COOH, M = 89.0 g mol⁻¹. For 0.890 g:

• n = 0.890 ÷ 89.0 = 0.0100 mol
• CH₃CH(NH₂)COOH + NaOH → CH₃CH(NH₂)COO⁻Na⁺ + H₂O
• n(NaOH) = 0.0100 mol, mass = 0.0100 × 40.0 = 0.400 g

Naming esters of amino acids

Alcohol part first, then the acid with “-oate”. Ethanol + alanine → ethyl 2-aminopropanoate, CH₃CH(NH₂)COOCH₂CH₃ (M = 117.0 g mol⁻¹). In the acidic mixture the NH₂ may be protonated, but write the ester with NH₂ when asked for the ester.

Amides: spot and classify

Feature	Primary amide	Secondary amide	Not an amide
Group	–CONH₂	–CONH–	amine, e.g. –CH₂NH– with no C=O on N
Carbons on N	1	2	—
Example	hexanamide, CH₃(CH₂)₄CONH₂	N-propylpentanamide, CH₃(CH₂)₃CONHCH₂CH₂CH₃	CH₃CH₂NHCH₂CH₃
Made from (6.1.3(f))	acyl chloride + ammonia	acyl chloride + primary amine	—

Method in steps:

1. Find the nitrogen.
2. Is a C=O carbon bonded directly to it? If not, it is not an amide.
3. Count all the carbon atoms bonded to that nitrogen, including the C=O carbon.
4. One carbon: primary. Two carbons: secondary.

Worked reminder: making each type

• Primary: (CH₃)₂CHCH₂CH₂COCl + 2NH₃ → (CH₃)₂CHCH₂CH₂CONH₂ + NH₄Cl (4-methylpentanamide)
• Secondary: (CH₃)₂CHCH₂CH₂COCl + 2CH₃NH₂ → (CH₃)₂CHCH₂CH₂CONHCH₃ + CH₃NH₃⁺Cl⁻ (N,4-dimethylpentanamide)

In both, the second mole of base removes the HCl. Writing “+ HCl” with one mole of base also balances.

The polyamides in 6.2.3 are linked by secondary amide groups. The same counting rule applies inside a long chain.

Optical isomerism: the essentials

• Optical isomerism is a type of stereoisomerism, alongside E/Z and cis–trans (4.1.3).
• It needs a chiral centre, meaning a carbon atom bonded to four different groups.
• The two isomers are mirror images that are non-superimposable: no rotation lines up every group.
• If any two groups on the carbon are identical, the mirror image is the same molecule.

3-D drawing checklist

1. Put the chiral carbon in the centre.
2. Draw two bonds in the plane of the page (plain lines).
3. Show one bond coming towards you (solid wedge) and one going away (hashed wedge), both on the side opposite the in-plane pair.
4. Draw a mirror line, then reflect: left and right swap, wedge stays wedge, hashed stays hashed.
5. Label every group on both isomers.

A swap of any two groups on one chiral centre produces the other isomer. Use it to check whether two drawings are the same molecule or a mirror-image pair.

Finding chiral centres: fast elimination

Carbon type	Can it be a chiral centre?
CH₃ or CH₂	No: two or more H atoms
C in C=C or C=O	No: only three groups
C with two identical chains (e.g. two ethyls)	No
CH with H and three different groups	Yes
C with four different non-H groups	Yes
Ring carbon	Yes only if the two ring paths differ and the other two groups differ too

Compare whole groups, not just the atom attached. CH₂CH₃ and CH₂CH₂CH₃ differ, even though both start with CH₂.

Worked reminder: three quick counts

• 2-methylhexanoic acid, CH₃(CH₂)₃C*H(CH₃)COOH: C2 has H, CH₃, C₄H₉, COOH → 1.
• 2,4-dichloropentane, CH₃C*HClCH₂C*HClCH₃: C2 and C4 each have H, Cl, CH₃ and the rest of the chain → 2.
• 4-methylcyclohexan-1-ol: the two ring paths from C1 are identical, and C4 also sits on a symmetrical ring → 0.

Must-know distinctions

• Amide vs amine: an amide has C=O on the nitrogen; an amine does not.
• Primary vs secondary amide: count carbons on N, not hydrogens.
• Salt with alkali vs salt with acid: sodium carboxylate (COO⁻Na⁺) vs ammonium chloride (NH₃⁺Cl⁻).
• Optical vs E/Z isomerism: optical needs a chiral centre; E/Z needs a C=C in which both carbons hold two unlike groups.
• Glycine vs other α-amino acids: glycine (R = H) has no chiral centre; the others do.

Quick self-test

1. Write the general formula of an α-amino acid.
2. Which reagent reacts with the NH₂ group of an amino acid: NaOH(aq) or HCl(aq)?
3. Give the reagent and conditions to turn alanine into its ethyl ester.
4. Calculate the mass of NaOH that reacts with 0.890 g of alanine.
5. Classify HCONHCH₂CH₃.
6. Classify C₆H₅CH₂CONH₂.
7. Define a chiral centre.
8. How many chiral centres are in 2-iodo-3-methylbutane, CH₃CHICH(CH₃)₂?
9. How many chiral centres are in 2,4-dichloropentane?
10. Explain why glycine has no optical isomers.
11. In a 3-D diagram, what does a hashed wedge show?
12. Two drawings of the same compound differ only in that two groups on the chiral centre have changed places. What is the relationship between them?

Answers

1. RCH(NH₂)COOH
2. HCl(aq); the nitrogen lone pair accepts H⁺.
3. Ethanol with concentrated H₂SO₄ as catalyst, heated.
4. 0.0100 mol × 40.0 = 0.400 g
5. Secondary amide (N-ethylmethanamide): N is bonded to the C=O carbon and an ethyl carbon.
6. Primary amide (2-phenylethanamide): only the C=O carbon is on N.
7. Any carbon with four different atoms or groups attached.
8. 1 (C2: H, I, CH₃ and CH(CH₃)₂; C3 has two CH₃ groups).
9. 2 (C2 and C4).
10. R is H, so the α-carbon has two H atoms and is not a chiral centre.
11. A bond pointing away from you, behind the page.
12. They are optical isomers (non-superimposable mirror images).

Where marks are usually lost

• Putting NH₃ instead of NH₂ in the general formula, or attaching R to nitrogen.
• Showing NaOH reacting at the NH₂ group, or HCl at the COOH group.
• Leaving Cl⁻ out of the ammonium salt, so the product has an unbalanced charge.
• Writing “acid catalyst” without “concentrated H₂SO₄”, or forgetting that esterification is reversible.
• Calling a compound with N but no C=O on the nitrogen an amide.
• Drawing four plain bonds, so the 3-D arrangement and the mirror relationship cannot be seen.
• Swapping left and right and also turning the wedge into a hashed bond: that is the original molecule rotated, not its mirror image.
• Marking the C=O carbon, a CH₂ or a ring carbon with two identical paths as chiral.
• Defining optical isomers as “mirror images” without “non-superimposable”.

Official syllabus

OCR A Level Chemistry A (H432) specification, Version 3.1 (May 2026), for first assessment in 2017, section 6.2.2 Amino acids, amides and chirality, learning outcomes (a) to (d). Published by OCR.