Compound A(C9 H12) absorbed 3 equivalents of H2 on catalytic...

Compound $A\left(C_{9} H_{12}\right)$ absorbed 3 equivalents of $H_{2}$ on catalytic reduction over a palladium catalyst to give $\mathbf{B}\left(\mathrm{C}_{9} \mathrm{H}_{18}\right) .$ On ozonolysis, compound A gave, among other things, a ketone that was identified as cyclohexanone. On treatment with $\mathrm{NaNH}_{2}$ in $\mathrm{NH}_{3}$, followed by addition of iodomethane, compound $\mathrm{A}$ gave a new hydrocarbon, $\mathrm{C}\left(\mathrm{C}_{10} \mathrm{H}_{14}\right) .$ What are the structures of $\mathrm{A}, \mathrm{B},$ and $\mathrm{C} ?$

Compound $A\left(C_{9} H_{12}\right)$ absorbed 3 equivalents of $H_{2}$ on catalytic reduction over
a palladium catalyst to give $\mathbf{B}\left(\mathrm{C}_{9} \mathrm{H}_{18}\right) .$ On ozonolysis, compound A gave, among other things, a ketone that was identified as cyclohexanone. On treatment with $\mathrm{NaNH}_{2}$ in $\mathrm{NH}_{3}$, followed by addition of iodomethane, compound $\mathrm{A}$ gave a new hydrocarbon, $\mathrm{C}\left(\mathrm{C}_{10} \mathrm{H}_{14}\right) .$ What are the structures of $\mathrm{A}, \mathrm{B},$ and $\mathrm{C} ?$

Key Concepts

Catalytic Hydrogenation

This reaction involves the addition of hydrogen (H?) to multiple bonds, typically in alkenes or alkynes, using a metal catalyst like palladium. The process reduces unsaturated bonds to saturated bonds, altering the degree of unsaturation in the molecule and consequently changing its physical and chemical properties.

Ozonolysis

Ozonolysis is a chemical reaction where ozone (O?) cleaves carbon–carbon double bonds, breaking them into carbonyl-containing fragments such as aldehydes or ketones. This reaction is a powerful tool for structural determination because it provides insight into the location of double bonds within the original molecule.

Base-Mediated Reaction and Alkylation

Strong bases like sodium amide (NaNH?) in liquid ammonia are used to deprotonate acidic hydrogen atoms or to generate carbanions, which can act as nucleophiles. When these reactive intermediates are treated with alkyl halides (such as iodomethane), alkylation occurs, effectively adding carbon groups to the molecular framework. This transformation is central in modifying molecular skeletons and in constructing complex molecular architectures.

Organic Structural Elucidation

This concept involves deducing the structure of an organic compound by analyzing the reactions it undergoes. By interpreting the outcomes of various chemical transformations—such as hydrogenation, ozonolysis, and alkylation—chemists can piece together the molecular skeleton, functional groups, and connectivity present in the unknown compound. This systematic approach is essential in organic synthesis and reaction mechanism determination.

Transcript

00:01 In problem 9 .3a, we are to find the structure of molecule a, b, and c, using the reactions given as clues.

00:11 Each reaction gives us a different clue to what the molecule could be.

00:16 But we'll start out by analyzing compound a.

00:22 Compound a has nine carbons, and if this were an alkan, we'd expect there to be 20 hydrogens.

00:31 We get this by multiplying the number of carbons by 2.

00:34 And then adding two more to this.

00:37 So we would expect there to be 20 hydrogens.

00:40 We are missing 8.

00:42 If we divide 8 by 2, we get the number of degrees of unsaturation.

00:48 So there are 4 degrees of unsaturation.

00:54 Abbreviated us for this video.

00:59 Then it is reduced using a palladium catalyst.

01:03 This would reduce all double and triple bonds to single bonds.

01:06 But in part b, there's still one degree of unsaturation missing.

01:13 We can see that we should have 20 carbon, hydrogens, we have 18.

01:18 So this has one degree of unsaturation.

01:26 This tells us that there is a ring.

01:29 In the second reaction, we can see that the ring is a cyclohexane and that there is going to be a double bond coming off of the ring because when you react ozone, it will cleave double bonds to ketones.

01:49 So we know that the molecule looks something like this...

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