At which position is nicotine's side chain attached to the pyridine ring?

The side chain is attached at position 3 of the pyridine ring, which is the β-position. Oxidation converts the side chain at this position into the carboxyl group of nicotinic acid.

What is the composition of the side chain in nicotine?

Subtracting the pyridine residue, C₅H₄N–, from nicotine's formula, C₁₀H₁₄N₂, gives a side-chain composition of –C₅H₁₀N.

What does the Herzig–Meyer estimation prove about nicotine?

Heating nicotine with hydriodic acid at 150–300 °C produces one mole of methyl iodide. Because nicotine contains no oxygen, this formation of CH₃I proves the presence of one N-methyl group.

What does zinc chloride distillation suggest about nicotine's side chain?

Zinc chloride distillation gives pyridine, pyrrole, and methylamine. The formation of pyrrole suggests that four carbon atoms and one nitrogen atom form a five-membered heterocyclic ring.

Why is nicotine's side-chain ring called pyrrolidine rather than pyrrole?

The side-chain unit has four more hydrogen atoms than N-methylpyrrole. These additional hydrogens indicate that the two double bonds of the pyrrole ring have been reduced, giving a saturated N-methylpyrrolidine ring.

What fragments are formed in Pinner's degradation of nicotine?

After bromination and hydrolysis with aqueous barium hydroxide, nicotine gives nicotinic acid, malonic acid, and methylamine.

What is the final systematic name and point of attachment in nicotine?

Pinner's proof establishes that the N-methylpyrrolidine ring is attached through its α-carbon, position 2. Combined with substitution at position 3 of the pyridine ring, the systematic name is 3-(1-methylpyrrolidin-2-yl)pyridine.

What does the consumption of two moles of methyl iodide by nicotine indicate?

Nicotine contains two primary amines

Nicotine contains one secondary amine

Nicotine contains no nitrogen atoms

At which position is the side chain attached to the pyridine ring in nicotine?

Position 1 (the nitrogen position)

What does the Herzig–Meyer estimation prove in the structure elucidation of nicotine?

The presence of a carboxyl group

The presence of two pyridine rings

Why is the side-chain ring assigned as pyrrolidine rather than pyrrole?

It has four extra hydrogen atoms and is saturated

It contains two additional oxygen atoms

It forms nicotinic acid on oxidation

Which set of fragments is obtained in Pinner's degradation of nicotine?

Nicotinic acid, malonic acid, and methylamine

Benzoic acid, acetic acid, and ammonia

Succinic acid, pyridine, and ammonia

What does the formation of malonic acid in Pinner's degradation establish?

The pyrrolidine ring is attached through its α-carbon

The pyridine ring is attached at position 3

Nicotine contains an oxygen atom

Both nitrogen atoms are primary

JAtone

Structure Elucidation of Nicotine

Nicotine has the molecular formula C₁₀H₁₄N₂ and contains two tertiary nitrogen atoms.
Oxidation gives nicotinic acid, proving a pyridine ring substituted at the β-position (position 3).
Degradation evidence identifies an N-methylpyrrolidine side chain.
Pinner’s proof establishes attachment through the α-carbon (position 2) of the pyrrolidine ring.
The systematic name is 3-(1-methylpyrrolidin-2-yl)pyridine.

Structure Elucidation of Nicotine

Introduction

Source: Nicotine is found in the leaves of Nicotiana tabacum (the tobacco plant).

Physical nature: It is a colourless, oily, levorotatory liquid and a highly toxic alkaloid.

Class: Pyridine–pyrrolidine alkaloid.

1. Molecular Formula

Elemental analysis and molecular-weight determination establish the molecular formula of nicotine:

C₁₀H₁₄N₂

2. Nature of the Nitrogen Atoms

Reaction with Methyl Iodide

When nicotine is treated with methyl iodide (CH₃I), it consumes two moles of CH₃I to form a dimethiodide (a diquaternary ammonium salt):

C₁₀H₁₄N₂ + 2 CH₃I → C₁₀H₁₄N₂ · 2 CH₃I

Deduction

Nitrogen has a maximum covalency of four bonds and can therefore form quaternary ammonium salts.

A primary amine (1°; –NH₂) requires three CH₃I molecules to form a quaternary salt.

A secondary amine (2°; –NH–) requires two CH₃I molecules.

A tertiary amine (3°; >N–) requires only one CH₃I molecule.

Nicotine contains two nitrogen atoms and consumes two CH₃I molecules, or one mole per nitrogen atom. Therefore, both nitrogen atoms are tertiary, and neither has a replaceable active hydrogen.

3. Presence of a Pyridine Ring

Oxidation with Acidic Potassium Dichromate

Vigorous oxidation of nicotine with acidic potassium dichromate (K₂Cr₂O₇ / H₂SO₄) or concentrated HNO₃ degrades the molecule and yields nicotinic acid (pyridine-3-carboxylic acid):

Nicotine (C₁₀H₁₄N₂) ⟶[O] Pyridine-3-carboxylic acid (nicotinic acid) + side-chain decomposition products

Nicotinic acid = pyridine-3-carboxylic acid

                 COOH
                   |
                  C3 (β)
                /       \
              C2         C4
              |           |
             N1           C5
                \       /
                  C6

Deduction

1.Nicotine contains a pyridine nucleus.

2.The side chain is attached specifically at the β-position (position 3) of the pyridine ring.

3.The pyridine ring survives vigorous oxidation while the side chain is oxidized to a –COOH group. Thus, the pyridine ring is the more stable nucleus.

4. Formula of the Side Chain

Subtracting the β-substituted pyridine residue (C₅H₄N–) from the molecular formula of nicotine gives:

C₁₀H₁₄N₂ − C₅H₄N = C₅H₁₀N

Conclusion: The side chain attached at position 3 of the pyridine ring has the composition –C₅H₁₀N.

5. Structure of the Side Chain

5.1 Presence of an N-Methyl Group

Herzig–Meyer estimation: Heating nicotine with hydriodic acid (HI) at 150–300 °C produces one mole of methyl iodide (CH₃I).

Nicotine contains no oxygen atoms, so methoxy or Zeisel-type ester splitting is ruled out. The formation of CH₃I therefore proves the presence of one N-methyl group (>N–CH₃).

>N−CH₃ + HI ⟶ >NH + CH₃I

After accounting for the N-methyl group, the side chain contains a four-carbon framework; its remaining composition is C₄H₇N.

C₅H₁₀N − CH₃ = C₄H₇N

5.2 Zinc Chloride Distillation

Distillation of nicotine over zinc chloride (ZnCl₂), followed by soda lime treatment, yields:

1.Pyridine.

2.Pyrrole.

3.Methylamine (CH₃NH₂).

The isolation of pyrrole, a five-membered unsaturated heterocyclic ring containing one nitrogen atom, suggests that the four carbon atoms and one nitrogen atom form a five-membered ring.

5.3 Saturation Level of the Ring

The molecular formula of an N-methylpyrrole is C₅H₇N.

The corresponding saturated side-chain unit contains four additional hydrogen atoms:

C₅H₁₁N − C₅H₇N = 4 H atoms

These four extra hydrogen atoms show that the two double bonds of the pyrrole ring have been completely reduced.

Conclusion: The side chain is an N-methylpyrrolidine ring.

6. Point of Attachment: Pinner’s Proof

The pyridine ring is linked at position 3 (the β-position), but the N-methylpyrrolidine ring can be linked in two possible ways:

Structure A — α-linkage: pyridine attached at C2′
3-pyridyl—C2′H—C3′H₂—C4′H₂—C5′H₂—N1′(CH₃)
          \_________________________________/
                    ring closure to C2′

Structure B — β-linkage: pyridine attached at C3′
3-pyridyl—C3′H₂—C2′H—N1′(CH₃)—C5′H₂—C4′H₂
          \_________________________________/
                    ring closure to C3′

Pinner’s Degradation Reaction

1.Nicotine is treated with bromine in acetic acid to yield dibromonicotine.

2.Dibromonicotine is hydrolyzed with aqueous barium hydroxide, Ba(OH)₂, at 100 °C.

3.The reaction yields three distinct fragments:

Nicotinic acid.

Malonic acid (HOOC–CH₂–COOH).

Methylamine (CH₃NH₂).

Chemical Logic

Malonic acid contains a continuous, unbranched three-carbon chain that is oxidized to the malonic-acid unit.

In Structure A (α-linkage), the three carbons between the nitrogen and the point of substitution form an unbroken, contiguous chain. Oxidative cleavage of this unit yields malonic acid.

In Structure B (β-linkage), the pyrrolidine-ring carbons are divided into disconnected one-carbon and two-carbon units, so Structure B cannot yield malonic acid.

Conclusion: The pyrrolidine ring is attached to the pyridine ring through its α-carbon (position 2).

7. Final Structure of Nicotine

All analytical and degradation evidence is consistent with the following structure:

The pyridine ring is substituted at position 3 (β-position).

The N-methylpyrrolidine ring is linked through position 2 (α-position).

Nicotine = 3-(1-methylpyrrolidin-2-yl)pyridine

                 C3′H₂────C4′H₂
                /             \
  3-pyridyl—C2′H               C5′H₂
                \             /
                  N1′────CH₃

The pyridine ring is attached to C2′ of the pyrrolidine ring.

Systematic Name

IUPAC name: 3-(1-methylpyrrolidin-2-yl)pyridine.

Alternative name: β-pyridyl-α-(N-methylpyrrolidine).

Nicotine has the molecular formula C₁₀H₁₄N₂ and contains two tertiary nitrogen atoms.
Oxidation gives nicotinic acid, proving a pyridine ring substituted at the β-position (position 3).
Degradation evidence identifies an N-methylpyrrolidine side chain.
Pinner’s proof establishes attachment through the α-carbon (position 2) of the pyrrolidine ring.
The systematic name is 3-(1-methylpyrrolidin-2-yl)pyridine.

Contents

About Structure Elucidation of Nicotine

Structure Elucidation of Nicotine is a fundamental concept in organic chemistry. Understanding the mechanisms, reaction conditions, and stereo-chemical outcomes is crucial for mastering organic chemistry. Our curated resources provide step-by-step visualizations to help you excel.

Structure Elucidation of Nicotine

Nicotine has the molecular formula C₁₀H₁₄N₂ and contains two tertiary nitrogen atoms.
Oxidation gives nicotinic acid, proving a pyridine ring substituted at the β-position (position 3).
Degradation evidence identifies an N-methylpyrrolidine side chain.
Pinner’s proof establishes attachment through the α-carbon (position 2) of the pyrrolidine ring.
The systematic name is 3-(1-methylpyrrolidin-2-yl)pyridine.

Structure Elucidation of Nicotine

Introduction

Source: Nicotine is found in the leaves of Nicotiana tabacum (the tobacco plant).

Physical nature: It is a colourless, oily, levorotatory liquid and a highly toxic alkaloid.

Class: Pyridine–pyrrolidine alkaloid.

1. Molecular Formula

Elemental analysis and molecular-weight determination establish the molecular formula of nicotine:

C₁₀H₁₄N₂

2. Nature of the Nitrogen Atoms

Reaction with Methyl Iodide

When nicotine is treated with methyl iodide (CH₃I), it consumes two moles of CH₃I to form a dimethiodide (a diquaternary ammonium salt):

C₁₀H₁₄N₂ + 2 CH₃I → C₁₀H₁₄N₂ · 2 CH₃I

Deduction

Nitrogen has a maximum covalency of four bonds and can therefore form quaternary ammonium salts.

A primary amine (1°; –NH₂) requires three CH₃I molecules to form a quaternary salt.

A secondary amine (2°; –NH–) requires two CH₃I molecules.

A tertiary amine (3°; >N–) requires only one CH₃I molecule.

Nicotine contains two nitrogen atoms and consumes two CH₃I molecules, or one mole per nitrogen atom. Therefore, both nitrogen atoms are tertiary, and neither has a replaceable active hydrogen.

3. Presence of a Pyridine Ring

Oxidation with Acidic Potassium Dichromate

Vigorous oxidation of nicotine with acidic potassium dichromate (K₂Cr₂O₇ / H₂SO₄) or concentrated HNO₃ degrades the molecule and yields nicotinic acid (pyridine-3-carboxylic acid):

Nicotine (C₁₀H₁₄N₂) ⟶[O] Pyridine-3-carboxylic acid (nicotinic acid) + side-chain decomposition products

Nicotinic acid = pyridine-3-carboxylic acid

                 COOH
                   |
                  C3 (β)
                /       \
              C2         C4
              |           |
             N1           C5
                \       /
                  C6

Deduction

1.Nicotine contains a pyridine nucleus.

2.The side chain is attached specifically at the β-position (position 3) of the pyridine ring.

3.The pyridine ring survives vigorous oxidation while the side chain is oxidized to a –COOH group. Thus, the pyridine ring is the more stable nucleus.

4. Formula of the Side Chain

Subtracting the β-substituted pyridine residue (C₅H₄N–) from the molecular formula of nicotine gives:

C₁₀H₁₄N₂ − C₅H₄N = C₅H₁₀N

Conclusion: The side chain attached at position 3 of the pyridine ring has the composition –C₅H₁₀N.

5. Structure of the Side Chain

5.1 Presence of an N-Methyl Group

Herzig–Meyer estimation: Heating nicotine with hydriodic acid (HI) at 150–300 °C produces one mole of methyl iodide (CH₃I).

Nicotine contains no oxygen atoms, so methoxy or Zeisel-type ester splitting is ruled out. The formation of CH₃I therefore proves the presence of one N-methyl group (>N–CH₃).

>N−CH₃ + HI ⟶ >NH + CH₃I

After accounting for the N-methyl group, the side chain contains a four-carbon framework; its remaining composition is C₄H₇N.

C₅H₁₀N − CH₃ = C₄H₇N

5.2 Zinc Chloride Distillation

Distillation of nicotine over zinc chloride (ZnCl₂), followed by soda lime treatment, yields:

1.Pyridine.

2.Pyrrole.

3.Methylamine (CH₃NH₂).

The isolation of pyrrole, a five-membered unsaturated heterocyclic ring containing one nitrogen atom, suggests that the four carbon atoms and one nitrogen atom form a five-membered ring.

5.3 Saturation Level of the Ring

The molecular formula of an N-methylpyrrole is C₅H₇N.

The corresponding saturated side-chain unit contains four additional hydrogen atoms:

C₅H₁₁N − C₅H₇N = 4 H atoms

These four extra hydrogen atoms show that the two double bonds of the pyrrole ring have been completely reduced.

Conclusion: The side chain is an N-methylpyrrolidine ring.

6. Point of Attachment: Pinner’s Proof

The pyridine ring is linked at position 3 (the β-position), but the N-methylpyrrolidine ring can be linked in two possible ways:

Structure A — α-linkage: pyridine attached at C2′
3-pyridyl—C2′H—C3′H₂—C4′H₂—C5′H₂—N1′(CH₃)
          \_________________________________/
                    ring closure to C2′

Structure B — β-linkage: pyridine attached at C3′
3-pyridyl—C3′H₂—C2′H—N1′(CH₃)—C5′H₂—C4′H₂
          \_________________________________/
                    ring closure to C3′

Pinner’s Degradation Reaction

1.Nicotine is treated with bromine in acetic acid to yield dibromonicotine.

2.Dibromonicotine is hydrolyzed with aqueous barium hydroxide, Ba(OH)₂, at 100 °C.

3.The reaction yields three distinct fragments:

Nicotinic acid.

Malonic acid (HOOC–CH₂–COOH).

Methylamine (CH₃NH₂).

Chemical Logic

Malonic acid contains a continuous, unbranched three-carbon chain that is oxidized to the malonic-acid unit.

In Structure A (α-linkage), the three carbons between the nitrogen and the point of substitution form an unbroken, contiguous chain. Oxidative cleavage of this unit yields malonic acid.

In Structure B (β-linkage), the pyrrolidine-ring carbons are divided into disconnected one-carbon and two-carbon units, so Structure B cannot yield malonic acid.

Conclusion: The pyrrolidine ring is attached to the pyridine ring through its α-carbon (position 2).

7. Final Structure of Nicotine

All analytical and degradation evidence is consistent with the following structure:

The pyridine ring is substituted at position 3 (β-position).

The N-methylpyrrolidine ring is linked through position 2 (α-position).

Nicotine = 3-(1-methylpyrrolidin-2-yl)pyridine

                 C3′H₂────C4′H₂
                /             \
  3-pyridyl—C2′H               C5′H₂
                \             /
                  N1′────CH₃

The pyridine ring is attached to C2′ of the pyrrolidine ring.

Systematic Name

IUPAC name: 3-(1-methylpyrrolidin-2-yl)pyridine.

Alternative name: β-pyridyl-α-(N-methylpyrrolidine).

Nicotine has the molecular formula C₁₀H₁₄N₂ and contains two tertiary nitrogen atoms.
Oxidation gives nicotinic acid, proving a pyridine ring substituted at the β-position (position 3).
Degradation evidence identifies an N-methylpyrrolidine side chain.
Pinner’s proof establishes attachment through the α-carbon (position 2) of the pyrrolidine ring.
The systematic name is 3-(1-methylpyrrolidin-2-yl)pyridine.

Contents

About Structure Elucidation of Nicotine

SELF TEST

Practice MCQs

Question 1 / 10Score: 0

What is the molecular formula of nicotine?

LEARNING SUPPORT

Structure
Elucidation of Nicotine FAQ

The molecular formula of nicotine is C₁₀H₁₄N₂, as established by elemental analysis and molecular-weight determination.

Nicotine consumes two moles of methyl iodide to form a dimethiodide. Since each tertiary nitrogen consumes one mole of CH₃I, this shows that both nitrogen atoms in nicotine are tertiary.

Vigorous oxidation of nicotine with acidic potassium dichromate or concentrated nitric acid gives nicotinic acid, also called pyridine-3-carboxylic acid. This proves that nicotine contains a pyridine nucleus.

Structure Elucidation of Nicotine

Structure Elucidation of Nicotine

Introduction

1. Molecular Formula

2. Nature of the Nitrogen Atoms

Reaction with Methyl Iodide

Deduction

3. Presence of a Pyridine Ring

Oxidation with Acidic Potassium Dichromate

Deduction

4. Formula of the Side Chain

5. Structure of the Side Chain

5.1 Presence of an N-Methyl Group

5.2 Zinc Chloride Distillation

5.3 Saturation Level of the Ring

6. Point of Attachment: Pinner’s Proof

Pinner’s Degradation Reaction

Chemical Logic

7. Final Structure of Nicotine

Systematic Name

About Structure Elucidation of Nicotine

Structure Elucidation of Nicotine

Structure Elucidation of Nicotine

Introduction

1. Molecular Formula

2. Nature of the Nitrogen Atoms

Reaction with Methyl Iodide

Deduction

3. Presence of a Pyridine Ring

Oxidation with Acidic Potassium Dichromate

Deduction

4. Formula of the Side Chain

5. Structure of the Side Chain

5.1 Presence of an N-Methyl Group

5.2 Zinc Chloride Distillation

5.3 Saturation Level of the Ring

6. Point of Attachment: Pinner’s Proof

Pinner’s Degradation Reaction

Chemical Logic

7. Final Structure of Nicotine

Systematic Name

About Structure Elucidation of Nicotine

Practice MCQs

StructureElucidation of Nicotine FAQ

Practice MCQs

StructureElucidation of Nicotine FAQ

Structure
Elucidation of Nicotine FAQ

Structure
Elucidation of Nicotine FAQ