Step-by-Step Guide for Organic Conversions

 We'll cover the following important steps of organic conversion

1. Step-Up Reactions (Increasing the carbon chain)
2. Step-Down Reactions (Decreasing the carbon chain)
3. Functional Group Interconversion (FGI) (Changing one functional group to another)
4. Rearrangement Reactions (Changing the position of the functional group)
5. Strategies for Multi-Step Conversions

1. Step-Up Reactions (Increasing Carbon Chain Length)

Step-up reactions help in increasing the number of carbon atoms in a given compound. These are commonly used when the target molecule has more carbons than the starting compound.

Methods of Step-Up Reactions:

1. Cyanide Addition (KCN or NaCN)

   • Alkyl halide → Alkyl cyanide
   • Example: CH₃Br + KCN → CH₃CN (Methyl bromide to acetonitrile)
   • Hydrolysis of cyanides gives carboxylic acids (CH₃CN → CH₃COOH).

2. Grignard Reagent with Carbon Dioxide

   • R-MgX + CO₂ → R-COOH
   • Example: CH₃MgBr + CO₂ → CH₃COOH (Methane to acetic acid)

3. Aldol Condensation (for ketones and aldehydes with α-Hydrogen)

   • CH₃CHO → CH₃CH=CHCHO

4. Acetoacetic Ester Synthesis (For ketones with increased chain length)

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2. Step-Down Reactions (Decreasing Carbon Chain Length)

Step-down reactions are used when the target molecule has fewer carbon atoms than the starting compound.

Methods of Step-Down Reactions:

1. Decarboxylation (Removal of –COOH Group)

   • R-COOH → R-H + CO₂
   • Example: CH₃COOH → CH₄ + CO₂

2. Oxidative Cleavage (Ozonolysis of Alkenes)

   • RCH=CHR → RCHO + R'CHO (Using O₃)

3. Haloform Reaction (For Methyl Ketones)

   • CH₃COCH₃ + I₂ + NaOH → CHI₃ + CH₃COO⁻Na (Acetone to CHI₃ and sodium acetate)

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3. Functional Group Interconversion (FGI)

Functional group interconversion is one of the most common requirements in organic conversions.

Common Interconversions:

1. Alcohol to Alkyl Halide

   • R-OH + PCl₅ → R-Cl + POCl₃ + HCl

2. Alcohol to Aldehyde/Ketone

   • R-OH + PCC → R-CHO (For 1° alcohols)
   • R-OH + PCC → R-CO-R' (For 2° alcohols)

3. Aldehyde to Carboxylic Acid

   • R-CHO + [O] → R-COOH

4. Carboxylic Acid to Alcohol (Reduction)

   • R-COOH + LiAlH₄ → R-CH₂OH

5. Amine Preparation (Hofmann Degradation, Gabriel Synthesis)

   • Amide + Br₂ + NaOH → Amine (Hofmann Degradation)

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4. Rearrangement Reactions (Changing Position of Functional Groups)

Sometimes, the target compound requires repositioning of a functional group.

Key Rearrangement Reactions:

1. Pinacol-Pinacolone Rearrangement (Vicinal diols to ketones)
2. Beckmann Rearrangement (Oximes to amides)
3. Wagner-Meerwein Rearrangement (Carbocation rearrangement)
4. Favorskii Rearrangement (α-Haloketones to carboxylic acids)

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5. Strategies for Multi-Step Conversions

For complex conversions, follow these strategies:

1. Compare the target and starting compound

   • Identify changes in carbon chain length.
   • Identify changes in functional groups.

2. Plan step-up or step-down accordingly

   • If more carbon atoms are needed → Use step-up reactions.
   • If fewer carbon atoms are needed → Use step-down reactions.

3. Choose the appropriate FGI

   • Identify intermediate compounds necessary for conversion.

4. Rearrange if needed

   • If functional groups are in the wrong position, use rearrangement reactions.

5. Use retrosynthetic analysis for complex problems

   • Break down the final compound into simpler intermediates.

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Example Conversion Problems

Q1: Convert Ethanol (C₂H₅OH) to Acetic Acid (CH₃COOH)
Solution:
Ethanol → Acetaldehyde → Acetic Acid

1. Oxidation: C₂H₅OH + [O] → CH₃CHO (PCC)
2. Further oxidation: CH₃CHO + [O] → CH₃COOH (KMnO₄ or K₂Cr₂O₇)

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Q2: Convert Benzene to p-Nitrophenol
Solution:
Benzene → Phenol → p-Nitrophenol

1. Nitration: C₆H₆ + HNO₃ → Nitrobenzene
2. Reduction: Nitrobenzene → Aniline (Sn/HCl)
3. Diazotization: Aniline + HNO₂ → Benzene diazonium chloride
4. Hydrolysis: C₆H₅N₂Cl + H₂O → Phenol
5. Nitration: Phenol + HNO₃ → p-Nitrophenol

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Organic conversions require a logical approach based on the number of carbons, functional groups, and their positions. Mastering step-up, step-down, functional group interconversion, and rearrangement reactions makes complex conversions easier.