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Chapter 9: Problem 10

Draw a structural formula for the most stable carbocation with each molecular formula. (a) \(\mathrm{C}_{4} \mathrm{H}_{9}{ }^{+}\) (b) \(\mathrm{C}_{3} \mathrm{H}_{7}^{+}\) (c) \(\mathrm{C}_{5} \mathrm{H}_{11}^{+}\) (d) \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{O}^{+}\)

Short Answer

Expert verified
Answer: The most stable carbocations for the given molecular formulas are: C4H9+: ``` H | H3C-C-CH2-CH3 | H ``` (tertiary carbocation with a positive charge on the central carbon atom) C3H7+: ``` H | H2C-C-CH3 | H ``` (secondary carbocation with a positive charge on the middle carbon atom) C5H11+: ``` H | H3C-C-CH2-CH2-CH3 | H ``` (tertiary carbocation with a positive charge on the central carbon atom) C3H7O+: ``` O || H3C-C-CH3 | H ``` (secondary carbocation with a positive charge on the middle carbon atom, stabilized by the oxygen atom through resonance)

Step by step solution

01

Understanding carbocations

A carbocation is a molecule that contains a positively charged carbon atom. They are highly reactive intermediate species in many organic reactions. Carbocations have only six electrons in their valence shell, making them electron-deficient and seeking to gain more electrons to become more stable.
02

Determining the stability of carbocations

The stability of carbocations can be determined using the following order: Tertiary (3°) > Secondary (2°) > Primary (1°) > Methyl (CH3+). This order is based on the ability of neighboring carbon atoms and alkyl groups to stabilize the positive charge through induction and hyperconjugation.
03

Step 3(a): Drawing the structural formula for C4H9+

To draw the most stable carbocation with the molecular formula C4H9+, we should choose a tertiary carbocation since it's more stable than secondary or primary carbocations. The structural formula for the most stable C4H9+ carbocation is: ``` H | H3C-C-CH2-CH3 | H ``` With a positive charge on the tertiary carbon atom (the central carbon atom).
04

Step 3(b): Drawing the structural formula for C3H7+

To draw the most stable carbocation with the molecular formula C3H7+, we should choose a secondary carbocation since there is no tertiary carbocation with three carbon atoms. The structural formula for the most stable C3H7+ carbocation is: ``` H | H2C-C-CH3 | H ``` With a positive charge on the secondary carbon atom (the middle carbon atom).
05

Step 3(c): Drawing the structural formula for C5H11+

To draw the most stable carbocation with the molecular formula C5H11+, we should choose a tertiary carbocation. The structural formula for the most stable C5H11+ carbocation is: ``` H | H3C-C-CH2-CH2-CH3 | H ``` With a positive charge on the tertiary carbon atom (the central carbon atom).
06

Step 3(d): Drawing the structural formula for C3H7O+

To draw the most stable carbocation with the molecular formula C3H7O+, we should choose a secondary carbocation, as the oxygen atom can stabilize the positive charge through resonance. The structural formula for the most stable C3H7O+ carbocation is: ``` O || H3C-C-CH3 | H ``` With a positive charge on the secondary carbon atom (the middle carbon atom).

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Most popular questions from this chapter

Each of these compounds can be synthesized by an \(\mathrm{S}_{\mathrm{N}} 2\) reaction. Suggest a combination of haloalkane and nucleophile that will give each product. (a) \(\mathrm{CH}_{3} \mathrm{OCH}\) (b) \(\mathrm{CH}_{3} \mathrm{SH}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{PH}_{2}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CN}\) (e) \(\mathrm{CH}_{3} \mathrm{SCH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{3}\) (f) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{NH}^{+} \mathrm{Cl}^{-}\) (h) \((R)-\mathrm{CH}_{3} \mathrm{CHCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (i) \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{OCH}\left(\mathrm{CH}_{3}\right)_{2}\) (j) \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{OCH}_{2} \mathrm{CH}=\mathrm{CH}_{2}\) (k) ClC1CCCCN1 (1) C1COCCO1

Which isomer of 1-bromo-3-isopropylcyclohexane reacts faster when refluxed with potassium tert-butoxide, the cis isomer or the trans isomer? Draw the structure of the expected product from the faster reacting compound.

The reaction of bromomethane with azide ion \(\left(\mathrm{N}_{3}{ }^{-}\right)\)in methanol is a typical \(\mathrm{S}_{\mathrm{N}} 2\) reaction. What happens to the rate of the reaction if \(\left[\mathrm{N}_{3}{ }^{-}\right]\)is doubled?

Alkenyl halides such as vinyl bromide, \(\mathrm{CH}_{2}=\mathrm{CHBr}\), undergo neither \(\mathrm{S}_{\mathrm{N}} 1\) nor \(\mathrm{S}_{\mathrm{N}} 2\) reactions. What factors account for this lack of reactivity?

Using your roadmap as a guide, show how to convert butane into 2-butyne. Show all reagents and all molecules synthesized along the wav.
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