CHM 1321A
Assignment 1 Answers
1) Draw Lewis structures, showing all unshared electrons, for the following covalent molecules:
(a) CH3NH2
(b) CH2CH2
(c) C2H2
H
H
C C
H
H
H C C H
(d) CH3CH2CHO
(e) CH3CH2OH2+
(f) (CH3)3N
H H
O
H C C C
H H H
H H
H C C O H
H H H
H
H
H C N C H
H
C H
H
H
H
(g) CH3CN
(h) CH3CH(OH)CH3
(i) CH3NCO
H
H C C N
H
H
H O H
H C C C H
H H H
H
H C N C O
H
(j) CH2CHCH(OH)CH2CO2H
(k) NCCH2COCH2CHO
(l) CH3CH(CH3)CH2C(CH2CH3)2CHO
H
H C N H
H H
H H H H O
C C C C C
H
O H O H
H
H O H O
N C C C C C
H
H
H
H
H C H
H C H
H H H
O
H C C C C C
H
H C H
H
H
H
H C H
H C H
H
(m) (CH3)3C+
(n) CH3CH2O-
(o) CH3CHCHCH2CHCHCOOH
H
H C H
H
H C C
H
H C H
H
H H
H C C O
H H
H H H H H H O
H C C C C C C C
O H
H
H
(p) HC(O)N(CH3)2
H
O
C
H H
C H
N
C H
H H
2) There is a small portion of the periodic table that you must know to do organic chemistry. Construct
this from memory including the group numbers, numbers of valence electrons, and electronegativities.
Note: Other texts may give slightly different values
I
H2.1
III
IV
V
VI
VIII
B2.0 C2.5 N3.0 O3.5 F4.0
Si1.8 P2.1 S2.5 Cl3.0
Br2.8
I2.6
3) Draw structures for
(a) Two compounds with the formula C4H10
CH3
H2
C
CH3
H3C
CH
C
H2
H3C
Butane
CH3
2-methylpropane
(b) Three compounds with the formula C3H8O2
(There may be other structures, check with your TA if you are not sure)
OH
H2
C
HO
OH
OH
Propane-1,2-diol
H2
C
HO
CH3
C
H2
Propane-1,3-diol
CH3
CH3
O
O
Dimethoxymethane
2-Methoxy-ethanol
CH3
O
Propane-1,1-diol
H2
C
H3C
O
C
H2
OH
CH
H3C
CH
HO
C
H2
C
H2
H2
C
H3C
OH
C
H3C
CH
HO
OH
CH3
Propane-2,2-diol
1-Methoxyethanol
(c) Two compounds with the formula C2H7N
H2
C
H
N
NH2
H3C
H3C
ethylamine
CH3
N,N-dimethylamine
(d) Five compounds of formula C3H6O
O
H2
C
O
C
H3C
Propanal
CH3
Propan-2-one
H
OH
H
C
H
C
OH
C
H2
H2C
C
H3C
OH
H3C
Prop-2-en-1-ol
C
H
Propen-1-ol
H2C
O
H2C
CH2
Propen-2-ol
CH3
H2
C
O
H2C
Oxacyclobutane
C
H2C
CH
CH3
Methyloxacyclopropane
H2C
CH
OH
Cyclopropanol
4) Name all the compounds in Question 3.
Answers in Red.
5) Show the direction of the dipole moments of the following bonds. Predict whether the dipole is
relatively large or small.
δ+ δ
δ+ δ
δ+
δ+
δδC
Cl
δ
δ
(b) C-H
(a) C-Cl
-
C
+
B
C
C
H
δ-
δ
N
H
N
(c) C-N
C
O
(d) C-O
+
(e) C-B
δ-
δ+
δ
δ
O
H
C
Br
+
-
(f) N-H
(g) O-H
(h) C-Br
6) Draw the important resonance forms and show the resonance hybrid structures for the following:
(a)
O
C
H3C
H3C
(b)
H3C
H3C
O
C
O
C
O
C
(c)
H3C
H3C
(d)
CH3
CH3
H3C
O
C
δ−
O
CH3
H3C
δ+
CH3
CH2
O
C
CH2
O
C
O
C
H3C
CH2
insignificant
H3C
O
C
δ−
O
CH2
H3C
NH2
NH2
H3C
O
C
NH2
H3C
O
C
δ−
O
δ C
H3C
NH2
δ+
+
NH2
OH
CH3
C
H3C
C
H2
H3C
O
C
δ−
CH2
H
C
H2
CH3
O H
CH3
C
C
H3C
H2
δ+ H
O
H3C
C
δ+ H
2
CH3
S
H2C
CH
H2C CH2
(e)
S
H2C
CH
H2C CH2
(f)
H
C
H2C
H2C
C
H2
H
C
H2C
H2C
C
CH2
H
C
H2C
H2C
(g)
H2C
H2C
(h)
C
H2
H
C
C
CH2
H
C
H2C
H2C
C
H2
CH2
C
CH2
H2C
H2C
Hδ- δCH2
C
C
CH2
C
H2
H2C
H2C
H
C
C
H2
CH2
C
CH2
H2C
H2C
Hδ+ δ+
CH2
C
C
CH2
C
H2
CH3
N
H2C
CH3
CH3
N
H2C
CH3
(i)
δ+
H2C
C
H2C CH2
CH2
C
CH2
CH2
C
H2
H2C
C
H2C CH2
CH2
C
CH2
CH2
C
H2
δ+
S
S
octets full - no resonance possible
CH3NO2
H3C
O
N
O
+2
N
H3C
O
O
H3C
O
N
δ−
O
δ N
O
H3C
δ−
+
O
insignificant
(j)
CH3COOH
H3C
O
C
O
H
H3C
O
C
O
H
H3C
O
C
O
H
δ−
O
δ C
H
O
H3C
δ+
+
7) For the following resonance forms, label the major and minor resonance forms, and show which ones
are of equal energy. Justify your choices.
(a)
H2
H3C C C N
H
H3C C C N
Minor
Major
All atoms have a full Octet. In the second structure, the negative charge is located on the more electronegative
atom.
(b)
O
C
H3C
C
H
H
C
CH3
H3C
Minor
O
C
C
H
H
C
H3C
CH3
O
C
H
C
C
H
CH3
Major
In the Major resonance structure, all atoms have a full octet, and none are charged.
In the minor resonance form, one carbon is lacking an octet, and there is a large separation between positive
and negative charges. The middle structure has one carbon lacking an octet, and there is a small separation
between positive and negative charges.This structure is intermediate between the other two.
(c)
H3C
O
C
O
C
H
C
H2
CH3
H3C
O
C
C
H
O
C
C
H2
CH3
H3C
O
C
C
H
Major
Minor
O
C
C
H2
CH3
Major
All atoms in all structures have a full octet.
in the Major (2 equivalent) resonance forms, the negative charge resides on the more electronegative oxygen
atom.
In the Minor resonance form, the negative charge resides on the less electronegative carbon.
(d)
H2
C
H3C
NH2
H3C
C
NH2
Minor
H2
C
NH2
H3C
C
NH2
H2
C
NH2
C
NH2
Major
Major
In the Major (2 equivalent) resonance forms, all atoms have an octet (this criterion overides having a positive
charge on a more electronegative atom).
In the minor resonance form, the positively charged carbon atom is lacking an octet.
8) For each pair of ions, determine which is more stable. Justify your answer in each case.
a)
(a)
H3C
H
C
CH3
or
H3C
H
C
OCH3
H3C
H
C
OCH3
Delocalization with the lone pairs of the oxygen stabilizes the second compound.
b)
H H
H2C C C CH3
H H2
H2C C C CH2
or
H H
H2C C C CH3
Delocalization with the electrons in the double bond stabilizes the first compound. In the second
compound, the double bond is too far away. The CH2 carbon has no lone pairs to donate to the positively
charged carbon.
c)
H2 C
CH3
or
H2 C
C
N
H 2C
C
N
Delocalization with the lone pairs of the nitrogen stabilizes the second compound.
d)
H2
C
H2
C
CH2
H2C
C
H2C
CH
CH2
CH
H2C
or
H2C
C
H2
CH
C
H
H2
C
CH2
C
H2C
H2C
CH
C
H2
Delocalization with the electrons in the double bond stabilizes the first compound. In the second
compound, the double bond is too far away. The CH2 carbon has no lone pairs to donate to the positively
charged carbon.
e)
CH3
H3C
CH3
H3C
N
CH
or
C
C
H3C
CH3
H3C
H3C
CH3
CH3
N
C
H3C
CH3
Delocalization with the lone pairs of the nitrogen stabilizes the first compound.
f)
O
C
H3C
O
or
CH3CH2O
O
C
H3C
O
Delocalization with the lone pairs of both oxygens stabilizes the first compound.
9) Draw the shape of s and p orbitals including phasing. Show the resulting shapes following sp, sp2 and
sp3 hybridization.
p
s
sp
p
s
s
p
s
p
sp2
p
p
p
sp3
10) Draw complete molecular orbital structures for the following molecules using the LCAO method.
Label the atomic orbitals used to make bonds. Label the bonds.
(b) CH3CO2H
(c) CH3CHCHCH2CH3
(d) CH3NO2
(e) CH3CN
(a) CH3CH2NH2
(f) CH3OCH3