Q: Rank the following carbocations in order of increasing stability: $\mathrm{CH_3^+}$, $\mathrm{H_2C=CH^+}$, $\mathrm{(CH_3)_3C^+}$.

$\mathrm{CH_3^+} < \mathrm{H_2C=CH^+} < \mathrm{(CH_3)_3C^+}$

Q: Which of the following best describes the difference between cis and trans isomers in cyclohexane chair conformations?

Cis isomers have both substituents axial or both equatorial, trans isomers have one axial and one equatorial.

Q: Which of the following molecules has an $E$ configuration at its double bond?

A molecule where the two highest priority groups are on opposite sides of the double bond.

Q: In the reaction of cyclohexene with HBr, which product is favored and why?

The product where Br adds to the more substituted carbon due to carbocation stability.

Q: Which of the following best describes a $\sigma$ bond?

A bond formed by the end-to-end overlap of orbitals along the internuclear axis.

Q: Which of the following is true about the resonance hybrid of acetate ion ($\mathrm{CH_3COO^-}$)?

The negative charge is equally distributed over both oxygen atoms.

Q: Which of the following statements about Newman projections is correct?

The staggered conformation is more stable due to minimized torsional strain.

Q: Which of the following best explains why $\mathrm{Cl_2CHCOOH}$ is a stronger acid than $\mathrm{CH_3COOH}$?

The chlorine atoms withdraw electron density, stabilizing the conjugate base.

Question 1

Which of the following statements best explains why the conjugate base of acetic acid ($\mathrm{CH_3COOH}$) is stabilized by resonance?

Accepted Answer

The negative charge is delocalized over both oxygen atoms through resonance, reducing reactivity.

Question 2

Given the molecule cyclohexanol, which of the following is the correct formal charge on the oxygen atom?

Accepted Answer

$0$

Question 3

Which of the following pairs of compounds are enantiomers?

Accepted Answer

Two molecules that are non-superimposable mirror images of each other.

Question 4

Rank the following carbocations in order of increasing stability: $\mathrm{CH_3^+}$, $\mathrm{H_2C=CH^+}$, $\mathrm{(CH_3)_3C^+}$.

Accepted Answer

$\mathrm{CH_3^+} < \mathrm{H_2C=CH^+} < \mathrm{(CH_3)_3C^+}$

Question 5

Which of the following best describes the difference between cis and trans isomers in cyclohexane chair conformations?

Accepted Answer

Cis isomers have both substituents axial or both equatorial, trans isomers have one axial and one equatorial.

Question 6

Which of the following acids is the strongest? 
A: $\mathrm{CH_3COOH}$ 
B: $\mathrm{ClCH_2COOH}$ 
C: $\mathrm{Cl_2CHCOOH}$ 
D: $\mathrm{CH_3CH_2COOH}$

Accepted Answer

C: $\mathrm{Cl_2CHCOOH}$

Question 7

Which of the following molecules has an $E$ configuration at its double bond?

Accepted Answer

A molecule where the two highest priority groups are on opposite sides of the double bond.

Question 8

What is the systematic IUPAC name for the following compound?

$\mathrm{CH_3CH_2CH(CH_3)CH_2CH_3}$

Accepted Answer

2-methylpentane

Question 9

In the reaction of cyclohexene with HBr, which product is favored and why?

Accepted Answer

The product where Br adds to the more substituted carbon due to carbocation stability.

Question 10

Which of the following best describes a $\sigma$ bond?

Accepted Answer

A bond formed by the end-to-end overlap of orbitals along the internuclear axis.

Question 11

Which orbital hybridization is present in the central carbon of ethene ($\mathrm{C_2H_4}$)?

Accepted Answer

$sp^2$

Question 12

Which of the following is true about the resonance hybrid of acetate ion ($\mathrm{CH_3COO^-}$)?

Accepted Answer

The negative charge is equally distributed over both oxygen atoms.

Question 13

Which of the following molecules contains a chiral center?

Accepted Answer

$\mathrm{CH_3CHClCH_2OH}$

Question 14

Which of the following statements about Newman projections is correct?

Accepted Answer

The staggered conformation is more stable due to minimized torsional strain.

Question 15

Which of the following best explains why $\mathrm{Cl_2CHCOOH}$ is a stronger acid than $\mathrm{CH_3COOH}$?

Accepted Answer

The chlorine atoms withdraw electron density, stabilizing the conjugate base.

Question 16

Which of the following is the correct assignment of R/S configuration for the chiral center in $\mathrm{CHClOH}$?

Accepted Answer

R configuration if the priorities are Cl > OH > CH > H and the sequence is clockwise.

Question 17

Which of the following bonds in ethyne ($\mathrm{C_2H_2}$) is a $\pi$ bond?

Accepted Answer

The bond formed by the sideways overlap of $p$ orbitals.

Question 18

Which of the following is a correct statement about the products of the acid-base reaction between acetic acid and methylamine?

Accepted Answer

The products are acetate ion and methylammonium ion.

Question 19

Which of the following best describes the effect of a ring flip in cyclohexane?

Accepted Answer

Axial substituents become equatorial and vice versa.

Organic Chemistry 243: Midterm 1 Study Guide – Core Concepts and Practice

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