Question

Draw the structure of a hydrocarbon that absorbs 2 molar equivalents of \(\mathrm{H}_{2}\) on catalytic hydrogenation and gives only butanedial on ozonolysis.

Short answer

Buta-1,3-diene (CH2=CH-CH=CH2) is the hydrocarbon.

Step-by-step solution

Understanding the Problem

The problem involves finding a hydrocarbon that absorbs 2 molar equivalents of hydrogen, which indicates the presence of two double bonds. During ozonolysis, this hydrocarbon must yield only butanedial, indicating its structure prior to reactions.

Determine Product from Ozonolysis

Ozonolysis typically cleaves double bonds, producing carbonyl compounds (aldehydes or ketones). In this case, the reaction gives butanedial, which is an aldehyde with the formula \( ext{OHC-CH}_2 ext{-CH}_2 ext{-CHO}\). This suggests the presence of specific double bonds in the original hydrocarbon.

Reverse Engineer from Product

For butanedial to be the sole product, the initial hydrocarbon must have double bonds at positions where they can be converted into the required aldehyde groups after cleavage. This implies a straight-chain hydrocarbon with double bonds in positions that, after cleavage, yield fully saturated fragments (2 carbon units per aldehyde).

Construct Potential Hydrocarbon

Given that butanedial is the sole product, a reasonable structure for the original hydrocarbon is buta-1,3-diene ( ext{CH}_2=CH-CH=CH_2). This structure has two double bonds and would absorb two equivalents of hydrogen.

Verify Structure with Reactions

Hydrogenation of buta-1,3-diene would saturate both double bonds, forming butane, confirming the uptake of two equivalents of hydrogen. Ozonolysis would cut at the positions of the double bonds, correctly forming butanedial, validating our proposed structure.

Key concepts

Catalytic Hydrogenation

Catalytic hydrogenation is a chemical reaction that involves the addition of hydrogen molecules (\(\mathrm{H}_{2}\)) to a compound in the presence of a catalyst. This process is primarily used to convert unsaturated hydrocarbons, which contain double or triple bonds, into saturated hydrocarbons, which have only single bonds. - **Catalysts Used:** - Common catalysts include platinum (Pt), palladium (Pd), or nickel (Ni). - These catalysts speed up the hydrogenation process without being consumed.- **Hydrogen Molecules:** - In the exercise, two molar equivalents of hydrogen mean that each equivalent refers to a single double bond being saturated. - Thus, two molar equivalents indicate that two double bonds are present for hydrogenation. Catalytic hydrogenation is commonly used in the food industry for the hydrogenation of vegetable oils to produce margarine and other spreads. It provides a straightforward method to fully saturate compounds, converting alkenes to alkanes as seen with buta-1,3-diene transforming into butane upon hydrogenation.

Butanedial

Butanedial is an organic compound with the formula \( ext{OHC-CH}_2- ext{CH}_2- ext{CHO}\). It is characterized by two aldehyde groups located at the ends of a four-carbon chain. - **Structure and Name Explanation:** - Aldehyde groups have the characteristic \(-CHO\) structure. - The prefix 'butane' indicates there are four carbon atoms in the chain. - 'Dial' indicates that there are two aldehyde groups present.- **Production via Ozonolysis:** - Ozonolysis is a reaction breaking double bonds to form two carbonyl compounds. - In this case, ozonolysis of a hydrocarbon yields butanedial, which shows the cleavage creates two identical aldehyde groups. Butanedial is a fundamental aldehyde compound used in organic synthesis and as an intermediate in various chemical reactions. Its formation reflects the strategic positioning of double bonds in the precursor hydrocarbon, ensuring complete conversion during ozonolysis.

Hydrocarbon Structure

Understanding the hydrocarbon structure is crucial when predicting reaction outcomes. Hydrocarbons are composed only of carbon and hydrogen atoms. They can be categorized based on bonding: - **Saturated Hydrocarbons (Alkanes):** - Contain only single bonds. - Example: Butane, produced after the hydrogenation of buta-1,3-diene. - **Unsaturated Hydrocarbons (Alkenes and Alkynes):** - Alkenes contain one or more double bonds. - Alkynes contain one or more triple bonds. The hydrocarbon structure must be carefully studied to determine how it reacts. In the exercise, the original hydrocarbon buta-1,3-diene contains two double bonds which direct the reaction pathways in both hydrogenation and ozonolysis. Recognizing these structural features allows chemists to predict how a molecule will behave under given conditions, like transforming into a saturated version with hydrogenation or breaking into particular aldehydes during ozonolysis.

Double Bonds

Double bonds are a type of covalent bond where two pairs of electrons are shared between two atoms, typically carbon atoms in organic compounds: - **Attributes of Double Bonds:** - They are represented by the symbol '= ='. - Double bonds are stronger than single bonds but weaker than triple bonds. - They create a planar configuration, affecting the geometry of the molecule. - **Role in Chemical Reactions:** - Double bonds are reactive sites in chemical reactions such as hydrogenation and ozonolysis. - In catalytic hydrogenation, each double bond can be converted to a single bond by adding hydrogen atoms. In the context of the exercise, the presence of two double bonds in buta-1,3-diene is the reason it requires two equivalents of hydrogen to become butane. Moreover, these double bonds are the precise locations where ozonolysis cuts the molecule to yield butanedial, demonstrating their pivotal role in determining the products of reactions.