karishma muthukumar ([email protected]) sarah ibrahim

Organic Chemistry Peer Tutoring Department CHEM 51CUniversity of California, Irvine Professor VanderwalWesley Vu ([email protected]) http://sites.uci.edu/ochemtutorsSarah Ibrahim ([email protected])Karishma Muthukumar ([email protected])

Midterm 2 Review Packet Key

1. Indicate the reagents:

The arrow to the right is a transesterification reaction. Transesterification is the process of goingfrom one ester to another ester. The alcohol reagent would need to contain the portion that isbeing replaced (-tBu). A strong acid (e.g. TsOH) would need to be included as well. The arrow tothe left is a hydrolysis reaction. Hydrolysis is the acid-catalyzed process of going from one esterto a carboxylic acid. A strong acid (e.g. HCl), water (to replace -OMe with -OH), and heat wouldbe required to undergo this reaction.

2. What are the starting materials?

A cyanohydrin can form upon addition of HCN to a carbonyl. Hydrolysis of the cyanohydrinyields a carboxylic acid. Looking at the product, the aldehyde is the best option for the startingcarbonyl.

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3. Indicate two ways of generating this product:

This is a Wittig reaction. Be familiar with Wittig reactions (starting materials, products,reagents). An alkene is generated from an aldehyde or ketone (in this case, an aldehyde) with atriphenyl phosphonium ylide. There are two possible carbonyl compounds paired with twopossible ylide combinations to generate the given product.

4. What reagents are necessary to convert this ester to a ketone?

First, the ester must be converted to an aldehyde. DIBAL-H is a suitable reagent for this ester →aldehyde conversion. This reduction is a preparatory step so that a Grignard or organolithiumcomponent could be added. Recall that a Grignard reaction is a reaction between an aldehyde orketone to form a secondary or tertiary alcohol. The product upon addition of the Grignard ororganolithium must be oxidized to form the ketone. PCC is a mild oxidizing agent. Strongeroxidizing agents are also possible for this reaction.



5. True/False: More reactive acyl compounds could be converted to less reactive acylcompounds by nucleophilic substitution.

This statement is true and is important to consider when conducting reactions and decidingwhether a reaction is a go or no. Generally, less reactive acyl compounds cannot be converted tomore reactive compounds. Keep in mind reactivity trends when performing substitutionreactions.

Least reactive to most reactive: amide → carboxylic acid ~ ester → anhydride → acid chloride

6. What conditions favor the formation of the kinetic enolate? Choose all that apply.

A. Strong bulky base (LDA)B. Strong nucleophilic base (KOC(CH3)3)C. Polar aprotic solvent (THF)D. Polar protic solvent (CH3CH2OH)E. Low temperature (-78 degC)F. Room temperature (25 degC)

The kinetic enolate is the enolate that is less stable but more quickly formed. There are certainconditions that favor this type of enolate. LDA is a strong bulky base that removes the mostaccessible proton on the less substituted carbon. The polar aprotic solvent helps to not protonateany rapidly formed enolate. The low temperature is also a key aspect that prevents the enolatefrom converting to the more stable thermodynamic enolate.

7. Which of the following reaction conditions is the most favorable for the formation of animine? Explain your answer. Additionally, predict the product of the reaction.

(a)

(b)



(c)

Answer: C. Formation of an imine involves attack of the carbonyl followed by elimination of theOH leaving group. Acidic conditions are required because protonation of OH makes it a betterleaving group. However, if conditions are too strongly acidic, the amine nucleophile will beprotonated. This protonated amine lacks a free electron pair and can no longer act as anucleophile.

8. What cyclic hemiacetal is formed from the intramolecular cyclization of each molecule?

(a)

(b)

Answers:

Tip: number your carbons so you don’t lose track of them. This will help you place substituentson your final ring.



(a)

(b)

9. Give the names for the following compounds.

(a)Propanoic anhydride. Anhydrides are named with the suffix -anhydride

(b)Cyclohexyl propanoate. Esters are named with the suffix -oate. The group attached directly tothe oxygen atom comes first.

(c)4-methylheptanenitrile. Nitriles are named with the suffice -nitrile.

(d)N-cyclopentylpentamide. Amides are named with the suffix -amide. Substituents attacheddirectly to the nitrogen atom are denoted using the prefix N-.

10. Rank the following protons in the indicated CH2 groups in order of increasing acidity.

(a)



(b)

(c)

Answer: C < B < A. More resonance stabilization = more stable conjugate base = stronger acid

11. What enolate is formed when each ketone is treated with LDA in THF? What enolate isformed when each ketone is treated with NaOCH3 in CH3OH?

(a)

(b)

(c)

Answers: LDA in THF promotes the formation of the kinetic enolate, while NaOCH3 in CH3OHpromotes the formation of the thermodynamic enolate

(a)

(b)



(c)

12. Draw the products of each reaction.

a.

b.

13. Devise a synthesis of each analgesic compound from phenol (C6H5OH) and any otherorganic or inorganic reagents.



14. Devise a synthesis of each compound using 1-bromobutane (CH3CH2CH2CH2Br) as theonly organic starting material. You may use any other inorganic reagents.



15. Draw the products formed (including stereoisomers) in each reaction.

a.

b.

16. The enolate derived from diethyl malonate reacts with a variety of electrophiles (not justalkyl halides) to form new carbon-carbon bonds. With this in mind, draw the products formedwhen Na+ -CH(CO2Et)2 reacts with each electrophile, followed by treatment with H2O.

a.

b.


karishma muthukumar ([email protected]) sarah ibrahim

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