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Q76.

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Organic Chemistry
Found in: Page 59

Short Answer

Question:

a. What is the hybridization of each N atom in nicotine?

b. What is the geometry around each N atom?

c. In what type of orbital does the lone pair on each N atom reside?

d. Draw a constitutional isomer of nicotine.

e. Draw a resonance structure of nicotine.

Answer

  1. The N atom that belongs to the six-membered ring is sp2 hybridized, and the one belonging to the five-membered ring is sp3 hybridized.
  2. The N atom present in the six-membered and five-membered rings has trigonal planar and tetrahedral geometry, respectively.
  3. The lone pair of electrons on N (six-membered ring) belongs to the sp2 -hybridized orbital, and the one on N (five-membered ring) belongs to the sp3 -hybridized orbital.
  4. The constitutional isomer of nicotine is shown be

e. The two resonance structures of nicotine are as follows:

See the step by step solution

Step by Step Solution

Step-by-Step Solution Step 1: Hybridization of nitrogen

The hybridization (mixing of orbitals) of an atom is determined by considering the number of atomic orbitals involved/participating in hybridization.

The nitrogen atom that is bonded to three other atoms and has a lone pair on it or is bonded to four other atoms is said to be hybridized.

The nitrogen atom attached to two other groups and bears a lone pair is said to be hybridized.

Step 2: Hybridization of the nitrogen atom in nicotine

Representation of the hybridization of nitrogen atoms in nicotine

The N atom in the nicotine molecule present on the six-membered ring is connected to two carbon atoms and contains a lone pair of electrons. Therefore, it is hybridized, and thus, the lone pair of electrons reside in the -hybridized orbital.

The N atom present on the five-membered ring is bonded to three carbon atoms and contains a lone pair of electrons on it, and therefore, it will be hybridized.

The lone pair on this nitrogen atom resides in the -hybridized orbital.

Step 3: Geometry and Hybridization

  • hybridization: Tetrahedral geometry.
  • hybridization: Trigonal planar geometry.
  • hybridization: Linear geometry.

The hybridized N atom has trigonal planar geometry, and the hybridized nitrogen atom has tetrahedral geometry.

Step 4: Constitutional isomer of nicotine

The molecules that bear the same molecular formula but adopt different structures are named constitutional isomers.

Interchanging the position of the methyl group present on -hybridized nitrogen atom with the hydrogen atom present adjacent to it gives the structure of the constitutional isomer of nicotine.

The constitutional isomer of nicotine

Step 5: Resonance structure of nicotine

The different structures used to describe the bonding in a molecule that cannot be described adequately using a single Lewis structure are termed resonance structures.

Nicotine has two resonance structures, which are given below:

Resonance structures of nicotine

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