1. Write the molecular formula of the compound nicotine: 2. What is the hybridiz
ID: 504815 • Letter: 1
Question
1. Write the molecular formula of the compound nicotine:
2. What is the hybridization of each N atom?
N of the six-membered ring:
sp
sp2
sp3
N of the five-membered ring:
sp
sp2
sp3
3. Describe the geometry about each N atom. (We are concerned only with the electron-domain geometry.)
The N of the six-membered ring is
tetrahedral
square planar
trigonal planar
trigonal pyramidal
The N of the five-membered ring is
tetrahedral
trigonal pyramidal
square planar
trigonal planar
Explanation / Answer
1) The percentage composition of nicotine is 74% carbon, 8.7% hydrogen and 17.3% nitrogen. Its molar mass is 162.26g/mol.
Get % into atomic ratios by ÷ by appropriate At Wt:
C: 74/12.011 = 6.16; H: 8.7/1.008 = 8.63; N: 17.3/14.01 = 1.23
Composition must be integers so divide through by the lowest value:
C 6.16/1.23 = 5.0; H = 8.63/1.23 = 7.0 N = 1.23/1.23 = 1
Empirical formula is C5H7N1 At Wt = 81.12
Molecular formula (C5H7N1)n 81.12 × n = 162.26 n= 2
Molecular formula of nicotine is C10H14N2
2)N of the five-membered ring is sp2.
The hybridization on nitrogen is sp2 only. For the pyridine nitrogen to form two pi bonds they both must be oriented perpendicularly. For the two pi bonds to be oriented perpendicularly, the two participating p-orbitals must be oriented perpendicularly.
b) N of the six-membered ring is sp2.
The nitrogen must have two unhybridized orbitals along the same direction, one orbital each can participate in pi-bonding on either side of the carbon atom. This is impossible since all the unhybridzed p orbitals are oriented mutually perpendicular to each other.
3) The N of the six and five -membered ring is trigonal planar
Trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle, called peripheral atoms. Trigonal planar are described as having sp2 hybridization.
The carbon and and the oxygen are bonded through a double bond which counts as "one electron pair". Hence the molecule has three electron pairs and is trigonal planar.
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