8A_S10_Worksheet5_key

8A_S10_Worksheet5_key - Chem 8A Worksheet 5 , Kai Concepts:...

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Unformatted text preview: Chem 8A Worksheet 5 , Kai Concepts: nucleophi|es electrophiles reaction coordinate diagrams reaction mechanisms alkene reactions carbocation stability reaction of alkynes Practice Problems: 1) Indicate whether each of the following molecules is more likely to behave as an electrophile or a nucleophile, and then explain your choice. (Put an “E” in the box if you think the molecule will behave like an electrophile and put an "N" in the box if you think the molecule will behave like a nucleophile.) The pi bonds make the (‘9 molecule electron rich c“30'42 the positive charge indicates that the oxygen is electron deficient because it wants to have two lone pairs instead of sharing electrons in a 3rd bond e0H the Na—C bond is an ionic bond. This means that the carbon is very electron rich NaCN CH3Li a The nitrogen atom has a lone pair and it is very electron rich and able to attack an electrophile H3C—NH2 BHs an N I. The carbon atom has a positive charge-— only 6 electrons and an empty p orbital. This is a very good electrophile because it is electron deficient The oxygen atom has a three lone pairs and a negative charge that indicate it have a build up of electron density. the CU bond is an ionic bond where the electropositive Li balances the negative charge on carbon. This means that the carbon is very electron rich The boron atom has only 6 electrons and an empty p orbital. This is a very good electrophile because it is electron deficient 2) Which of the following molecules is the best nucleophile? Circle your answer and provide a brief explanation. / / ><OH ><o/ The best nucleophile will have the most electron density available to “attack” an electrophile, so we compare the electron density on each oxygen. All three oxygen atoms have lone pairs and polar bonds to oxygen, but we see that the O-Na bond is actually ionic, which means that the Na+ is just balancing a negative charge on oxygen. 3) Consider the following reaction steps. Label which compound is the nucleophile and which is the eiectrophile in the reaction step, draw any relevant lone pair electrons, and then draw curved arrows showing the electron movement between the reagents. CH3 CH3 a) H.\O,H + /K/CH3 H C CH3 . .‘ H3C ® 3 ,O\ nucleophilevledrophile H GB H 69 b Br en 0‘ ’ 13 + zq—cm —» Br” ‘cHa electrophile V nucleophile N e 9 V nucleophile electrophile 4) Consider the following reaction: major product ////\///v flh N + /\/\C' a. What are the possible products? The major product? b. What is the name ofthe carbon intermediate that forms in this reaction? carbocation c. Draw the reaction mechanism using curved arrows. 5) Consider the reaction coordinate diagram below to answer the following questions: How many intermediates are present in 2 the following reaction diagram? l Free energy (G) How many transition states are present in the following reaction diagram? 3 Which is more stable, reactants or D —______________. products? _____.. I progress of reaction p r0 d J Cts 6) Draw and label the reaction coordinate diagram for the reaction presented in question 4, A) /\/ + HCI Free energy (6) B) \ B /\/ + ZCIC A G) C) c , (Bi Reaction progress 7) Which of the carbocations in the following pair is more stable? Briefly explain your answer. Both carbocations are stabilized by resonance delocalization of pi electrons, but B is a secondary carbocation while A is primary /\CH2 VS Wei-I3 69 (9 Both the O and N can donate electrons to stabilize the carbocation, but N is better at donating electron density because it is less electronegative H C\ ,CH vs 3 o 2 8) Determine the total number of pi bonds and/or rings for the following hydrocarbons: C10H16 C40H56 a 9) Draw the structure for each of the following: a. 2-hex ne V /V b. 4—bromo-1-octyne V r \ B r c. 4,4—dimethyI-1—pentyne /\'< % r x \ 10) Give the major product(s) for the fo|lowing reactions: Br I CH3CH2CH2C L Br excess HBr I —--—---+ Blr / /\\Y// H2 < II PVC .\\_,_.-"‘ a.» H H I —-12——’- \ —— cit: alkene /——-:-=:——/ Lindlar . dd“! catalyst > / e / O I \ H9804 H (k + ———+ —CH2CHQCH3 + \\ / corrected , x < ‘\ ‘fi‘ /L—CH2CH2’CCH2CH3 ...
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This note was uploaded on 06/27/2010 for the course CHE CHE 8A taught by Professor David during the Spring '09 term at UC Davis.

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8A_S10_Worksheet5_key - Chem 8A Worksheet 5 , Kai Concepts:...

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