2120 CHM Assignment #1 In this assignment: - Lewis structures, formal charge - Electronegativity, dipoles - Resonance - Acid/base 1. Draw the following molecules as full Lewis structures. Many molecules below possess a charge that is not showncalculate the formal charge on each atom and indicate the location of the charge where applicable. Hint: each atom has a full octet, so start by adding electrons to each atom to complete its octet. The only atoms we will encounter in this course that lack an octet are carbon (a carbocation lacks an octet) and metals (B, Al, Mg, Li, etc).
example: SH2 H H HH C C H H SH H Formal charge (FC) = # valence electrons in neutral atom - # bonds - # lone electrons For the carbons: FC = 4 - 4 - 0 = 0 (the carbons are all neutral in this molecule) For the sulfur: FC = 6 - 3 - 2 = +1 (so a "+" is placed beside the S) C H H C C H H H
a)
O
f)
Ph
O
b)
O
H g)
NH Et
c) PhO
O
h)
Me
N
H Me
d)
O
H i) C O Note: the central carbon does not possess lone pairs.
e)
OH2
j) O-t-Bu
k) N H
Assignment 1 - Review
2. Circle the plausible structures and put an X through the impossible structures below: Note: lone pairs should be added as required in order to satisfy the formal charge shown.
C C C Me C C
N
N
N
N
O
O 2+
O
O
B
B
2- B
3. For the following bonds, a. Show the direction of the dipole moment using two methods. b. Is the bond ionic polar or covalent? Example: C-H
+ - + Method 1: and indicate PARTIAL negative and PARTIAL positive C H charges; the formal charge of each atom is ZERO. Method 2: an arrow points toward the more electronegative atom; there is a "+" sign at the base of the arrow, under the more electropositive atom
i. ii. iii. iv. v. vi. vii. viii. ix. x. xi.
C-B Li-C Mg-C Li-O C-Br C-N N-Br O-Cl O-H S-H N-H
2
Assignment 1 - Review 4. For the following molecules: a. Draw the important resonance forms using arrows to show the movement of electrons b. Show the resonance hybrid structures
(a)
H3C O C CH3
(b)
H 3C
O C
CH2 H C C H
(c)
H3C
O C
NH2 H C C H CH2 C CH
OH (d) H C C C CH3 3 H2 CH3 N H 2C CH3
(e)
H2C CH H2C CH2
S
(f) HC HC
C CH
CH2
(g)
HC HC
(h)
(i)
CH3NO2
(j)
CH3COOH
(k)
H3C
O C
C H
H C
(l) CH3 CH2
5. Draw the direction of the dipole in the indicated bonds in each of the following molecules.
O
CH3 N
a) H3C
Cl
b) H3C
MgBr
c)
d)
e) HO
Cl
f) I
Cl
6. Write equations for the following reactions using arrow notation. Predict whether the reaction will favor the starting materials or products and justify your choice.
O S O OH H
a)
+
Br N
h)
H
S
+
b)
+
i)
CH3CO2
+
CF3CO2H
c)
OH H
+
HBr
j) H3C
H3C
O
d) e)
O
+
NH
k)
H H3C Li H3C
CF3OH
+
CF3CH2O
l) f)
OH2 Br
+ m) O H3C CH3 Lithium diisopropylamide (LDA) Li N
g)
H2SO4
+
HNO3
3