Chemistry 21 Homework set 5

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