Chem 21
Homework set 5
Now is a good time to learn some nomenclature — let's start with alkanes, alkenes, and alkynes,
with and without attached halogens. Everything you need is in sections 5.1 through 5.7. This
will be on the upcoming exam. Please keep in mind that you will be not be expected to name
molecules, but to interpret names and draw structures. This means that you still have to know
the vocabulary and a little about the procedure for numbering and naming molecules, but you
don't have to concern yourself with IUPAC's nit-picky rules about alphabetizing etc.
End-of-chapter problems from Hornback: Ch 5: I can't find any I want to assign. If you like, you
can pick out the parts relevant to drawing structures from names. Some of the "naming"
problems can be turned around — go from the name in the Study Guide to the struct in the text.
In addition to the names for the core structures (C1 thru C12; see prefixes in table 5.3), both
acyclic and cyclic, be sure that you know the structures, names, and abbreviations for the
common substituents isopropyl, tert-butyl, and phenyl. You should also know vinyl and allyl
(these don't have common abbreviations). It would be nice to also know the difference between
isobutyl and sec-butyl, and what neopentyl looks like, but I won't probe for this info on the exam
(meaning, of course, that (1) now you're curious and will immediately look these up, and (2) one
glance and they'll be permanently burned into your memory along with the 723 Pokemon™
creatures that you still remember from when you were 4 years old).
Ch 6: 15-17, 20-28, 31-33.
1. Draw these in skeletal notation. (Just break 'em down part-by-part, and be systematic.)
(a)
(b)
(c)
(d)
tert-butylcyclopentane
1,1,2-trichloro-2,4-dimethylpentane
2,2-dichloro-5-ethyl-4-isopropyloctane
1-cyclobutyl-2-fluoro-6-phenylhexane
a few complex substituents... these are always numbered starting from the point of attachment
(#1) and traveling out along the main substituent chain or around the substituent ring.
(e) 1-(1,3,3-tribromobutyl)-1-chlorocycloheptane
(f) 3-(chloromethyl)-1,1-dimethylcyclobutane
(g) 4-(1-ethylcyclopropyl)nonane
alkEnes and alkYnes...
(h) 2-isopropyl-1-pentene
(i) 1-phenyl-2-butyne
(j) 3,3-dimethyl-1-vinylcyclopentene
(k) 2-chloro-1-hepten-4-yne
and a bit of stereochemistry just for extra fun...
(note the different uses of cis and trans illustrated by the next two)
(l) trans-1,3-diallylcyclopentane
(m) cis-4-methyl-1-phenyl-1-pentene
of course E and Z are more proper stereochemical labels for double bonds...
(n)
(o)
(p)
(q)
(Z)-1-bromo-1-cyclopropyl-3-methyl-1-butene
(3Z,5E)-1,3,5-nonatriene
(Z)-3-phenyl-2-hexen-5-yne
3-(2-cyclobutenyl)-1-pentyne
2. Draw all the possible stereoisomers of the compound below. Think about where
stereochemistry is an issue and what combinations could exist. Label the double bonds in your
structures E or Z as appropriate.
O
Br
3. Compared to aniline, Ph–NH2, meta-nitroaniline is a weaker base, and para-nitroaniline is
weaker still. Explain. The pKas of the conjugate acids (anilinium ions) are given below. Note
the structure of the nitro group.
NH2
conjugate
acid pKas
NH2
O2N
NH2
O
O2N
4.6
2.46
NO2
N
1.01
O
4. Write a flow chart for the separation of the compounds below using liquid-liquid extraction.
Assume that the mixture is dissolved in Et2O to begin. In addition to water, your lab is stocked
with aq HCl, NaOH, and NaHCO3 (pKa of H2CO3 is 6.3). The pKas that you can't easily estimate
are given.
O
N
NH2
OH
O
HO
pKa = 20
pKa = 10
conj acid pKa = 4.1
Chem 21
Fall 2009
HW set 5
25 points; due Wed, Oct 14
Name _________________________________________
1. The structure below is intentionally drawn in a way that does not show stereochemistry.
Draw all the possible stereoisomers in skeletal notation. Don't attempt to show conformations;
keep the ring flat. Think about the places in the structure where stereochemistry is an issue and
the possible combinations.
Cl
CH2
CH
CH Br
2. Draw the following compounds in skeletal notation. Show stereochemistry where necessary.
Don't abbreviate substituents — you need to demonstrate knowledge of the structures here!
(a) trans-3-isopropyl-5-phenylcyclopentene
(b) 2-tert-butyl-1-hexen-5-yne
(c) (E)-3-(1-cyclobutenyl)-1,3-hexadiene
3. Write a flow chart for the separation of the compounds below using liquid-liquid extraction.
Draw structures to clearly show what compound is present at each step of the process and its
protonation state.
Assume that the mixture is dissolved in Et2O to begin. In addition to water, your lab is stocked
with aq HCl, NaOH, NaHCO3 (pKa of H2CO3 is 6.3). Hint: This isn't as difficult as it might
appear — think about what will be protonated with acid and what will be deprotonated with the
two bases.
OH
pKa = 9.7
pKa = 8.6
NC
CO2H
OH
H2N
conj acid
pKa = 5.0
pKa = 4.5
HO
pKa = 10.5