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.
e. The two resonance structures of nicotine are as follows:
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.
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.
The hybridized N atom has trigonal planar geometry, and the hybridized nitrogen atom has tetrahedral geometry.
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
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
Question: Stalevo is the trade name for a medication used in Parkinson’s disease, containing L-dopa, carbidopa, and entacapone.
a. Draw a Lewis structure for entacapone.
b. Which C–C bond in entacapone is the longest?
c. Which C–C single bond is the shortest?
d. Which C–N bond is the longest?
e. Which C–N bond is the shortest?
f. Use curved arrows to draw a resonance structure that is an equal contributor to the resonance hybrid.
g. Use curved arrows to draw a resonance structure that is a minor contributor to the resonance hybrid.
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