ChemistryChapter 21: Organic Synthesis
Growing the Chain (nitrile Named)
Haloalkane + CN- (ethanolic KCN named in many books) -> nitrile, one extra carbon.
Learning objectives
- Explain growing the chain (nitrile named) in simple chemical language.
- Connect 1. step-up with 2. hazard using equations, observations, or trends where needed.
- Answer a short Federal Board question with the correct terms and a clear reason.
Definition
Haloalkane + CN- (ethanolic KCN named in many books) -> nitrile, one extra carbon. Hydrolyse nitrile: carboxylic acid (acidic) or carboxylate (alkali). Reduce nitrile: amine (named hydride or H2). Meaning: C1 to C2 acid is a classic exam (bromomethane -> ethanenitrile -> ethanoic). Cyanide is toxic — named reagent, hazard slogan, not a student method to run, not a poison recipe. CN- substitution on halogenoalkane adds one carbon; nitrile reduced to amine or hydrolysed to acid. Count carbons after each synthetic step; silent carbon loss is the most common multi-step mistake.
Important terms
- GROWING THE CHAIN (NITRILE NAMED)
- Haloalkane + CN- (ethanolic KCN named in many books) -> nitrile, one extra carbon.
- 1. STEP-UP
- Count carbons in the target acid.
- 2. HAZARD
- Cyanide: poison slogan, specialist conditions, medical emergency if exposure.
Overview
Why CN-, then the hazard:
Step-Up
Count carbons in the target acid. If one more than the haloalkane you have, use nitrile. Then hydrolyse. Draw both steps. Grignard adds R group to carbonyl — carbon count rises.
Examples KCN named · Hydrolyse named · Ethanoic from bromomethane
Hazard
Cyanide: poison slogan, specialist conditions, medical emergency if exposure. These notes never describe how to generate HCN gas or to dose anyone. Exam: write KCN(eth) as the book does. Wittig named for alkene from carbonyl — optional name only.
Examples Toxic slogan · Not a method · Hospital if exposure
WHAT — GROWING THE CHAIN (NITRILE NAMED)
Haloalkane + CN- (ethanolic KCN named in many books) -> nitrile, one extra carbon. Hydrolyse nitrile: carboxylic acid (acidic) or carboxylate (alkali). Reduce nitrile: amine (named hydride or H2). Meaning: C1 to C2 acid is a classic exam (bromomethane -> ethanenitrile -> ethanoic). Cyanide is toxic — named reagent, hazard slogan, not a student method to run, not a poison recipe. CN- substitution on halogenoalkane adds one carbon; nitrile reduced to amine or hydrolysed to acid. Count carbons after each synthetic step; silent carbon loss is the most common multi-step mistake.
WHY — Why this topic matters
GROWING THE CHAIN (NITRILE NAMED) is an independent FBISE learning unit because students must use its definitions, conditions, equations, or trends separately in explanations and calculations.
HOW — How it works
STEP-UP: Count carbons in the target acid. If one more than the haloalkane you have, use nitrile. Then hydrolyse. Draw both steps. Grignard adds R group to carbonyl — carbon count rises. Examples: KCN named; Hydrolyse named; Ethanoic from bromomethane. HAZARD: Cyanide: poison slogan, specialist conditions, medical emergency if exposure. These notes never describe how to generate HCN gas or to dose anyone. Exam: write KCN(eth) as the book does. Wittig named for alkene from carbonyl — optional name only. Examples: Toxic slogan; Not a method; Hospital if exposure. Worked C1 to C2 acid: CH3Br + CN- -> CH3CN hydrolyse CH3CN -> CH3COOH named steps; cyanide hazard slogan, not a how-to
Worked example
- Worked C1 to C2 acid:
- CH3Br + CN- -> CH3CN
- hydrolyse CH3CN -> CH3COOH
- named steps; cyanide hazard slogan, not a how-to
In simple words
Named step-up. No cyanide how-to, no poisons.
Key points
- CN- adds one carbon
- then hydrolyse to acid
- +1 carbon
- name + warning
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Growing the Chain (nitrile Named)
Sticky Notes · Quick Revision
Core Idea
- Haloalkane + CN- (ethanolic KCN named in many books) -> nitrile, one extra carbon. Hydrolyse nitrile: carboxylic acid (acidic) or carboxylate (alkali). Reduce nitrile: amine (named hydride or H2). Meaning: C1 to C2 acid is a classic exam (bromomethane -> ethanenitrile -> ethanoic). Cyanide is toxic — named reagent, hazard slogan, not a student method to run, not a poison recipe. CN- substitution on halogenoalkane adds one carbon; nitrile reduced to amine or hydrolysed to acid. Count carbons after each synthetic step; silent carbon loss is the most common multi-step mistake.
1. STEP-UP
- Count carbons in the target acid. If one more than the haloalkane you have, use nitrile. Then hydrolyse. Draw both steps. Grignard adds R group to carbonyl — carbon count rises.
- KCN named
- Hydrolyse named
- Ethanoic from bromomethane
2. HAZARD
- Cyanide: poison slogan, specialist conditions, medical emergency if exposure. These notes never describe how to generate HCN gas or to dose anyone. Exam: write KCN(eth) as the book does. Wittig named for alkene from carbonyl — optional name only.
- Toxic slogan
- Not a method
- Hospital if exposure
Exam Example
- Worked C1 to C2 acid:
- CH3Br + CN- -> CH3CN
- hydrolyse CH3CN -> CH3COOH
- named steps; cyanide hazard slogan, not a how-to
Common Misconceptions
- Do not confuse 1. STEP-UP with 2. HAZARD; state the difference before giving an example.
- Writing only “CN- adds one carbon” is not enough. Explain what it means in a complete sentence.
FBISE Exam Check
- Explain growing the chain (nitrile named), compare its two main parts, and include the correct chemical evidence.
- Named step-up. No cyanide how-to, no poisons.
60-second revision
- Haloalkane + CN- (ethanolic KCN named in many books) -> nitrile, one extra carbon.
- 1. STEP-UP: Count carbons in the target acid.
- 2. HAZARD: Cyanide: poison slogan, specialist conditions, medical emergency if exposure.
- Exam reminder: Worked C1 to C2 acid: CH3Br + CN- -> CH3CN hydrolyse CH3CN -> CH3COOH named steps; cyanide hazard slogan, not a how-to
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