Organic Chemistry Practice Problems and Answers

Organic chemistry practice problems help you to learn organic chemistry properly in the beginning. Following aspects of organic chemistry are covered in these practice problems.

• Organic reactions
• Isomerism
• IUPAC nomenclature are covered in those problems.
• Physical properties of organic compounds such as melting and boiling points, acidic organic compounds, basic organic compounds.

Refer your notes when doing these problems. It will help you to understand organic chemistry very well.

What will be covered?

After the problems of section wise, there are collection of problems which covers all lessons of organic chemistry (school level).

These questions will cover preparing different compounds, reactions, physical properties and nomenclature. Also, different type of question styles (MCQ, Essay, True and False statements) are here to practice for you.

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How these problems are made and how do you do them?

Hydrocarbons

Under hydrocarbons, your knowledge about alkane, alkene, alkyne and benzene are tested.

Question

Are following statements are true or false about alkenes?

1. Alkenes are always unsymmetrical due to double bond.
2. When any alkene react with dilute sulfuric acid, secondary alcohols are given.
3. Carbon atoms which are connected to double bond have sp² hybridization.
4. Alkenes can be oxidized to carboxylic acids by acidic KMnO₄.
5. Platinum is more efficient catalyst than nickel in alkene hydrogenation.
6. Alkenes which shows Geometric Isomerism will show optical isomerism too.

Answers

1. False. Ethene, 2-butene are some examples to symmetrical alkenes.
2. False. According to the structure of alkene, given alcohol may vary. Ethene will give ethanol, a primary alcohol.
3. True.
4. True. But, carbon chain is broken. As products, ketones are also possible like carboxylic acids.
5. True
6. False. There is no need to show Geometric Isomerism when an organic compound show optical isomerism.

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Question

A group of students was a given a organic chemistry problem which was aimed to identify an organic compound X with C₆H₁₂ molecular formula. X is an aliphatic organic compound. Students have done several experiments to identify what is the correct structure (isomer) for that compound. For that, their experiments and observations are listed below.

• First experiment: X is mixed with dilute sulfuric acid and gives product Y. Then they have observed a reaction between given product Y and sodium. In this reaction, they had understood that, hydrogen gas was formed in second reaction.
• Second experiment: Then, they added anhydrous ZnCl₂ and concentrated HCl to check the turbidity by suspecting this Y is an alcohol. Y immediately gave a turbidity.
• Third experiment: From another experiment, they have discovered that, Y shows optical isomerism and X shows geometric isomerism.

Identify X and Y compounds.

Answer

• Though C₆H₁₂ follows C_nH_2n formula (general formula of alkene), C₆H₁₂ is an alkene.
• Due to release of hydrogen gas with sodium, Y should be an acidic compound. There are acidic organic compounds such as alkynes with acidic hydrogen, alcohols, phenol, carboxylic acids which have the capability of react with sodium.
  
  
• In the problem, it is given that C₆H₁₂ is a hydrocarbon. Because X reacts with dilute sulfuric acid (hydrolysis), X should be an alkene (alkynes are not hydrolyzed by sulfuric acid). When alkene reacts with dilute sulfuric acid, an alcohol is given. So Y should be an alcohol.
  
  
• Anhydrous ZnCl₂ and concentrated HCl is the Lucas Reagent which is used to identify the type of alcohol. In the second experiment, students are trying to identify the alcohol (Y). From observations, they will know Y is a tertiary alcohol because tertiary alcohol gives the turbidity immediately.
  
  
• From the third experiment, understanding Y shows optical isomerism, we can figure out the structure of Y.

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Problem

Fill following blanks by writing correct organic compounds and reagents to prepare 1-propanol from 2-propanol.

Hint: Use your knowledge of alkene. (knowledge of alcohols may be also helpful).

Answer: How 1-propanol is prepared from 2-propanol?

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Problem

How do you convert ethene to ethyne. Fill blanks with suitable organic compounds and reagents.

Hint: Use knowledge of alkene, alkyne, and alcohols

Answer: Steps of how ethanol is converted to ethyne (acetylene)

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Problem

Complete following diagram by giving correct compounds and reagents to synthesis ethane-1,2-diol. Acetylene is given as the only organic compound.

Alkene, alkyne knowledge is enough.

Answer: Steps of preparing ethane from ethanol

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Problem

There are different methods to prepare ethane from ethanol. Fill given blank squares with correct compounds and reagents. In this exercise, one way has an extra step in preparing ethane.

Hint: Use knowledge of alkane, alkene, alkyne, alkyl halide, grignard reagent and alcohols

Answer: Steps of preparing ethane from ethanol

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Problem

Draw all possible isomers for C₄H₈ and write their IUPAC names. Exclude cyclic isomers

Answer: Structure, chain, geometric isomers of C₄H₈

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Problem

Are there isomers for C₄H₁₀? If possible draw all of them and name them according to the isomer type. Exclude cyclic isomers if there are cyclic isomers.

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Problem

A hydrocarbon (X) within C₅H₈ molecular formula was been tested by following experiments.

X is treated with aqueous sulfuric acid and mercuric sulfate. Then given organic product is separated from the mixture. Y shows optical isomerism. When sodium is added to Y, hydrogen gas was emitted. Identify two organic compounds X and Y.

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Problem

An alkyne (A) has a molecular formula of C₆H₁₀. This alkyne does not emit a gas with sodium metal. When A reacts with hydrogen gas in the presence of Pt and and Lindlar catalyst, an alkene is given. Given alkene shows geometric isomerism. Both alkyne and alkene show optical isomerism. Identify structure of organic compound A.

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Practice Multiple choice Questions of alkane, alkene and alkyne

What is the incorrect statement of hydrolysis of C3H6 by sulfuric acid.

1. A secondary alcohol is given as the product.
2. Product shows optical isomerism.
3. Sulfuric acid behave as a catalyst.
4. Given product reacts with sodium.

1-butene and 2-butene are isomers of C₄H₈. What are the fault statements of followings?

1. Both of them give same product when they are hydrolyzed with dilute sulfuric acid.
2. Both compound show geometric isomerism.
3. Their physical and chemical properties are exactly the same.
4. Both compounds can reduce orange colour of liquid bromine in the CCl4 medium.

What is the most correct statement for alkene and alkyne?

1. All alkynes emit hydrogen gas with sodium because there is an acidic hydrogen atom in alkene compound.
2. Alkynes can be converted to alkene by hydrogen gas in the presence of platinum catalyst.
3. Alkenes and alkynes are hydrolyzed to carbonyl compounds in the presence of HgSO₄ and H₂SO₄.
4. All carbon atoms in the alkenes show sp² hybridization.

Practice problems and answers of benzene

Problem

Ethanol and benzene are very famous compounds in the organic chemistry. They have so many uses in the industrial scale. In this problem, you should prepare benzene from ethanol. Write it as a organic conversion and it is required to write reagents, reactants and physical conditions. It is okay to benzene is given as one compound in the product mixture in the final step.

Answer: how ethanol is converted to benzene

Problem

Explain the mechanism of benzene nitration. In the nitration mixture, there is a catalyst. What is that catalyst? Starting from benzene, how do you synthesis p-promoaniline?

Answers

Learn nitration of benzene and mechanism (C₆H₆ + HNO₃ + H₂SO₄ )

Sulfuric acid is the catalyst used in the benzene nitration. After the reaction, add sulfuric acid amount remains same.

Benzene to p-bromoaniline conversion

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Practice problems of halogen substituted organic compounds

Problem

If you are said to synthesis ethylmagnesium bromide (a grignard reagent compound) from ethanol, what are the steps you want to follow? Write each steps mentioning required reagents.

Answer

Ethanol to ethylmagnesium bromide

1. Add HBr to ethanol. It will give bromoethane.
2. Then, in the ether medium, add magnesium to the bromoethane. It will produce ethyl magnesium bromide.

Problem

In which mediums or which groups, it is impossible to synthesis grignard reagent?

Answer: Grignard reagent cannot be synthesized in aqueous or acidic or basic mediums.

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Problem

What is correct about phenylmagnesium bromide?

1. Phenylmagnesium bromide hydrolysis to phenol in the water.
2. Bromobenzene in the dry ether is synthesized with magnesium to preapre phenylmagnesium bromide.
3. By mixing phenylmagnesium bromide and methylchloride, toluene can be prepared.
4. Phenylmagnesium bromide is highly unstable in the water.

Answer

1. False: Phenylmagnesium bromide hydrolysis in the water. But it does not give phenol as the product. Benzene is the product.
2. Correct
3. Correct
4. Correct: See explanation given in the first choice.

Problems based on oxygen substituted organic compounds

Problem

There is an organic compound with a molecular formula C₄H₁₀O₂. 1 mol of this compound reacts with 1 mol of sodium. This organic compound show optical isomerism. Also, with anhydrous ZnCl₂ and concentrated HCl, no turbidity is given in first 30 minutes. Identify the correct structure of organic compound.

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Problem

X, an acidic organic compound reacts with sodium, aqueous sodium hydroxide and aqueous sodium bicarbonate. When compound is treated with LiAlH₄ , Y is given. Y only reacts with sodium. When 1 mol of Y is burnt in excess oxygen, 3 mol of carbon dioxide mol are given. What are the possible compounds suitable for X and Y

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Problem

An aromatic organic compound A, has a molecular formula of C₇H₉O₂. This compound reacts with aqueous NaOH and that reaction rises the temperature of the flask. Also given organic product is labeled as B. After that reaction, sodium is added to test the acidity of given product. An emission of gas can be seen and gas is tested for further experiments. Emitted gas was a combustible gas. When bromine liquid is added to A, orange colour of bromine liquid is reduced with time.

Problem

There are several statements about propanone and propanal. Which of them are true?

1. Though propanone is oxidized to propanoic acid, propanal cannot be oxidized.
2. Treating with LiAlH₄, propanone gives a compound which shows optical isomerism.
3. Treating with LiAlH₄, propanal gives a compound which shows optical isomerism.
4. Propanone and propanal shows similar reactions.

Problem

Carboxylic acids show acidic characteristics in the water. From following statements, what is correct about carboxylic acids?

1. Carboxylic acids have enough acidic strength to react with sodium hydroxide.
2. Ethanoic acid is more acidic than formic acid in aqueous states.
3. Phenols are more acidic than carboxylic acids because phenol can spread electrons of OH group in the benzene ring.
4. Ethanoic acid in dilute HCl solution will increase the dissociation of ethanoic acid.

Answer

1. Correct. Carboxylic acid reacts with aqueous NaOH and produce salt and water.
2. False. Formic acid has higher Ka value than ethanoic acid.
3. False. Carboxylic acids are more acidic than phenols. Phenol does not react with aqueous Na₂CO₃ or aqueous NaHCO₃
4. False. When strong acid such as HCl, H₂SO₄ exist with a weak acid as a aqueous solution, dissociation of weak acid decreases than when weak acid exists alone in the water.

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Practice problems of amine and amide

Problem

There is an amine (A) which has the molecular formula of C₃H₉N. When this amine is treated with aqueous sodium nitrite and cold dilute HCl mixture, B is given. B reacts with sodium and emit hydrogen gas. Also B responses so slowly to the Lucas' reagent. Identify A and B.

Problem

According to the type of amine, they react differently with nitrous acid (aqueous sodium nitrite and cold dilute HCl mixture).

Primary amine reacts with nitrous acid and give alcohols. Alcohols readily reacts with sodium and emit hydrogen gas. Primary alcohols reacts so slowly with Lucas' reagent.

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Problems and Questions covering all organic chemistry lessons

This question series will check your knowledge of all organic compounds, isomers, acidic, basic characteristics and many more.

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Write correct reagent to convert one organic compound to another. (These conversions are single step ones)

1. Carboxylic acid to alcohol
2. Alcohol to aldehyde
3. Amide to amine
4. Alkene to alcohol
5. Alkyne to aldehyde or ketone
6. Alkyne to aldehyde
7. Alkyl halide to alcohol
8. Amine to alcohol
9. Alcohol to alkyl halide
10. Alcohol to carboxylic acid
11. Carboxylic acid to carboxylic acid chloride by

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Problem

This question contains different sections of organic chemistry. You can check yourself after doing this question whether you have practiced enough in organic chemistry.

X is an organic compound which may be an aromatic or aliphatic. After studying following observation of X, you have to decide, what is the structure of X.

Answer

You should identify correct isomer of C₈H₁₀O according to the given details. Each observation will give an idea about the compound. Lets see some of them.

• X gives a turbidity with anhydrous zinc chloride and concentrated HCl. This test is called "Lucas test". When turbidity is given about 10 minutes, X compound should be an secondary alcohol.

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