organic synthesis problems and solutions pdf

Chemistry Steps

Organic Chemistry

Organic synthesis problems.

Organic Chemistry Practice Problems can be found after each topic covered in Chemistry Steps. The list of topics can be found here , and below are some examples of what you will find.

Organic Chemistry 1 Synthesis Problems

Nucleophilic substitution and elimination reactions, practice problems.

Predict the mechanism as SN1, SN2, E1 or E2 and draw the major organic product formed in each reaction. Consider any regioselectivity and stereoselectivity where applicable:

Answers and Solutions

Reactions of Alkenes Practice Problems

This is a comprehensive problem that covers the following topics and will serve as a review of all of them:

Substitution and elimination reactions.  Particularly,  substitution and elimination reactions of alcohols , the  regio – and stereochemistry of E2 reactions, and E2 reaction of cyclohexanes .

Mesylation and tosylation in Substitution and elimination reactions. 

Hydrohalogenation of alkenes according to Markovnikov’s rule .

Radical hydrohalogenation of alkenes .

Hydroboration-Oxidation of Alkenes .

Halogenation of alkenes through halohydrin formation .

Syn and anti dihydroxylation of alkenes.

Elimination reactions: Zaitsev and Hoffman products .

Ozonolysis of Alkenes.

Attempt to solve the entire problem before accessing the answers!

The  answers  will give you the structure of the  final product(s) only . Use this as a hint to determine the compounds formed after the first and second reactions.

Complete the following synthesis by adding the missing reagent(s) for each step and the structures for compound A and B:

Reactions of Alkynes Practice Problems

On the following synthetic scheme, identify the reagents, in the correct order, that you would use to achieve the following synthetic transformations. Determine the structure of compounds A and B and the major organic products resulting from the alkyne.

Organic Chemistry 2 Practice Problems

Alcohols practice problems.

Predict the major organic product(s) for the following Grignard reactions of a ketone, aldehyde, ester, carbon dioxide and an epoxide:

The Diels-Alder Reaction Practice Problems

For each Diels–Alder reaction, predict the major product(s) with correct stereochemistry when each cyclic  diene is reacted with a dienophile:

Aromatic Substitution Practice Problems

Show how each compound can be synthesized from benzene and any other organic or inorganic reagents.

The order of reactions is very important!  So, before every step,  consider the ortho – ,  para – ,  or meta directing effect  of the current group on the aromatic ring.

Devise a synthesis of each of the following compounds using an arene diazonium salt. They all require more than one step and you may select the desired regioisomer (for example the para product from an ortho, para mixture) when needed.

Aldehydes and Ketones Practice Problems

Predict the major product(s) obtained when each of the following compounds undergoes hydrolysis in the presence of an acid:

 Carboxylic Acids and Their Derivatives Practice Problems

Predict the  major organic product(s)  for each of the following reactions. They  all involve carboxylic acid derivatives  such as  esters, acid chlorides, nitriles, anhydrides, and amides . You may also need to go over the reactions covered in earlier chapters, particularly, the  Grignard  and  Gilman  reagents,  oxidizing  and  reducing   agents  and  electrophilic aromatic substitutions .

A link to each topic encountered in a given problem will be provided in the answer tab.

Alpha Carbon Chemistry – Enols and Enolates Practice Problems

This is a comprehensive practice problem  on the alpha carbon chemistry. The topics covered range from the simple halogenation reactions of enols to  multistep synthetic transformation .

To correctly answer these questions, you need to review the main principles of enolate chemistry – direct enolate alkylation, aldol condensation, crossed aldol condensation, alkylation using acetoacetic ester synthesis, malonic ester synthesis, the Stork enamine synthesis, Claisen condensation, Michael addition, and Robinson annulation.

CS Prime membership will also grant you access to multiple-choice quizzes !

If you are towards the end of your Organic 2 semester having covered most of the topics and ready for some more challenging synthesis problems – you are in the right place! In these practice problems, we will go over multistep organic synthesis.

Check also our new synthesis puzzles!

Go ahead and give it a try!

Determine the structure of each unknown in the following synthesis problems:

Keep in mind that it is rare to perform synthesis where only one product is formed and most often there is a need for isolating and purifying the desired product. So in this set of problems, you can choose a route where the target product is obtained as a mixture, even though it is desirable to design a synthesis where the yield of the target compound is in a reasonable range.

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By joining Chemistry Steps, you will gain instant access to the answers and solutions for all the Practice Problems including over 20 hours of problem-solving videos, Multiple-Choice Quizzes, Puzzles, and t he powerful set of Organic Chemistry 1 and 2 Summary Study Guides .

Check Also:

• Carboxylic Acids and Their Derivatives Practice Problems
• Acetals as Protecting Groups for Aldehydes and Ketones
• How to Choose Molecules for Doing SN2 and SN1 Synthesis-Practice Problems
• Alkene Reactions Practice Problems
• Changing the Position of a Double Bond
• Changing the Position of a Leaving Group
• Alkenes Multi-Step Synthesis Practice Problems
• Alkyne Synthesis Reactions Practice Problems
• Radical Halogenation in Organic Synthesis
• Grignard Reaction in Organic Synthesis with Practice Problems
• Ortho Para Meta Directors in Electrophilic Aromatic Substitution with Practice Problems
• Orientation in Benzene Rings With More Than One Substituent

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Browse Course Material

Course info, instructors.

• Dr. Kimberly Berkowski
• Prof. Timothy F. Jamison

Departments

As taught in.

• Organic Chemistry

Learning Resource Types

Organic chemistry ii.

You are leaving MIT OpenCourseWare

9.9 An Introduction to Organic Synthesis

9.9 • An Introduction to Organic Synthesis

As mentioned in the introduction, one of the purposes of this chapter is to use alkyne chemistry as a vehicle to begin looking at some of the general strategies used in organic synthesis—the construction of complex molecules in the laboratory. There are many reasons for carrying out the laboratory synthesis of an organic compound. In the pharmaceutical industry, new molecules are designed and synthesized in the hope that some might be useful new drugs. In the chemical industry, syntheses are done to devise more economical routes to known compounds. In academic laboratories, the synthesis of extremely complex molecules is sometimes done just for the intellectual challenge involved in mastering so difficult a subject. The successful synthesis route is a highly creative work that is sometimes described by such subjective terms as elegant or beautiful .

In this book, too, we will often devise syntheses of molecules from simpler precursors, but the purpose here is to learn. The ability to plan a successful multistep synthetic sequence requires a working knowledge of the uses and limitations of many different organic reactions. Furthermore, it requires the practical ability to piece together the steps in a sequence such that each reaction does only what is desired without causing changes elsewhere in the molecule. Planning a synthesis makes you approach a chemical problem in a logical way, draw on your knowledge of chemical reactions, and organize that knowledge into a workable plan—it helps you learn organic chemistry.

There’s no secret to planning an organic synthesis: all it takes is a knowledge of the different reactions and some practice. The only real trick is to work backward in what is often called a retrosynthetic direction. Don’t look at a potential starting material and ask yourself what reactions it might undergo. Instead, look at the final product and ask, “What was the immediate precursor of that product?” For example, if the final product is an alkyl halide, the immediate precursor might be an alkene, to which you could add HX. If the final product is a cis alkene, the immediate precursor might be an alkyne, which you could hydrogenate using the Lindlar catalyst. Having found an immediate precursor, work backward again, one step at a time, until you get back to the starting material. You have to keep the starting material in mind, of course, so that you can work back to it, but you don’t want that starting material to be your main focus.

Let’s work several examples of increasing complexity.

Worked Example 9.1

Devising a synthesis route.

How would you synthesize cis -2-hexene from 1-pentyne and an alkyl halide? More than one step is needed.

The product in this case is a cis-disubstituted alkene, so the first question is, “What is an immediate precursor of a cis-disubstituted alkene?” We know that an alkene can be prepared from an alkyne by reduction and that the right choice of experimental conditions will allow us to prepare either a trans-disubstituted alkene (using lithium in liquid ammonia) or a cis-disubstituted alkene (using catalytic hydrogenation over the Lindlar catalyst). Thus, reduction of 2-hexyne by catalytic hydrogenation using the Lindlar catalyst should yield cis -2-hexene.

Next ask, “What is an immediate precursor of 2-hexyne?” We’ve seen that an internal alkyne can be prepared by alkylation of a terminal alkyne anion. In the present instance, we’re told to start with 1-pentyne and an alkyl halide. Thus, alkylation of the anion of 1-pentyne with iodomethane should yield 2-hexyne.

Worked Example 9.2

How would you synthesize 2-bromopentane from acetylene and an alkyl halide? More than one step is needed.

What is an immediate precursor of an alkene? Perhaps an alkyne, which could be reduced.

What is an immediate precursor of a terminal alkyne? Perhaps sodium acetylide and an alkyl halide.

The desired product can be synthesized in four steps from acetylene and 1-bromopropane.