rganic hemistry II (E325) REVIEW PRBLEMS Key 1. Draw a complete orbital picture for the molecule shown below. Is this molecule chiral? Explain. 3 3 sp3 orbital p orbital sp2 orbital s orbital molecule is chiral - it has a non-superimposable mirror image 2. For each of the following compounds, draw the important resonance structures. a. ( 3 ) 2 N N 2 ( 3 ) 2 N N 2 ( 3 ) 2 N N 2 ( 3 ) 2 N N 2 b. 2 N 2 N 2 N c.
3. Indicate the direction of polarity for each of the bonds indicated: 3 3 3 Mg 4. Give IUPA names for each of the following compounds: 3 2 3 3 2 3 3 4-ethyl-4,6-dimethyl-2-heptyne l I (E)-2-chloro-4-iodo-2-butene (S)-2-methyl-3-isopropylcyclohexene 1-bromo-3-methylpentane N 2 o-nitrophenylbenzene l 2 3 4-chloro-3-ethylbenzoic acid
5. Identify the functional groups in the following molecules. amine alkene N 2 alcohol alkene l halide (chloride) arene N 3 ether amide alkyne ester 6. Using Newman projections, show all possible conformations of 1-bromobutane. Identify the lowest and highest energy conformations. 2 3 2 3 3 2 3 2 lowest energy highest energy 7. Draw the two possible chair conformations of the following molecules. In each case, identify the lowest energy conformation, and explain your reasoning. compound 3 possible conformations 3 3 3 3 3 3 3 3 A B A is the low energy conformation - two equatorial Me groups in A whereas in conformation B there are two axial methyl groups 3 3 3 3 3 3 3 3 3 A B A is the low energy conformation - since the group is sterically smaller than a methyl group, the steric interaction between axial & 3 groups in A is less severe than that in B (between two axial 3 groups)
8. define the following terms, and give an example of each: a. nucleophile: can donate electron density to an electron deficient species examples: :N 3, PhS -, =, etc. b. electrophile: can accept electron density from an electron rich species examples: 2, R 3 -X, +, etc. 9. Show all possible stereoisomers of the following compound. Note that there are 3 stereogenic centers. Identify the relationship of each of these isomers with one another, e.g. enantiomers, diastereomers, etc. N 2 N 2 N 2 N 2 N 2 A E G N 2 N 2 N 2 N 2 B D F enantiomers: A/B, /D, E/F, G/ all other pairs are diastereomers 10. Assign the absolute configuration of each stereogenic center present in the molecule shown below. 3 S S R 2 3
11. Write a complete mechanism to explain the following observation: 3 l 3 l l 3 3 2 3 3 + 3 3 3 3 3 major product minor product a l 3 3 3 2 l 3 3 3 2 methyl shift 3 3 3 2 2 cation l b (path a) 3 cation (more stable) (path b) trap by chloride 3 l 3 3 3 l 3 3 3 3 minor product major product 12. Predict all products from the following reactions. Label major and minor products. l 2 K ethanol (1 equiv.) A + B NaN 2 N 3 NaN 2 D 3 2 E 1. B 3 2. 2 2 2 Lindlar Pd F G
l 2 Na major A + B minor D 2 3 2 2 3 E F G 13. For each of the following transformations (A - D), the major product is shown. In each case, explain why the product formed is the major one. It may help to consider what minor products may be formed. 3 3 3 3 2 3 + 2 S 4 heat 3 3 2 l 4 A B 3 3 K ethanol D 3 3 A: Protonation of the double bond in A leads to a tertiary carbocation which is then trapped by water to give the more highly substituted alcohol B (Markovnikov addition) B: Dehydration of the tertiary alcohol leads to formation of the more highly substituted double bond via an E1 elimination (Zaitsev's rule). : Anti addition of bromine across the carbon-carbon double bond (e.g. formation of a bromonium ion intermediate, followed by backside displacement to give the anti product. D: E2 elimination requires anti orientation of proton and leaving group (trans-diaxial orientation of and ). In this case, anti elimination of a proceeds so that the more hichly substituted double bond in formed. In the elimination of b, anti elimination leads to formation of the least highly subtituted double bond.
3 b 3 anti elimination of and a leads to more highly substituted double bond anti elimination if not possible - c is equatorial c a anti elimination of and b leads to less highly substituted double bond 14. An unknown compound had the following MS: a) identify the base peak and the parent ion in this spectrum base peak: m/z = 43 parent ion: m/z = 72 b) what is the formula weight of this compound? FW = 72
15. Match a structure from the list below to the following IR spectra. learly identify and label diagnostic absorbances in each IR. A B D a. ompound: D sp3 - = b. ompound: B sp2 -