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MIDTERM EXAM: ORGANIC
CHEMISTRY 2026/2027 QUESTIONS
WITH VERIFIED ANSWERS &
COMPLETE RATIONALES
## SECTION 1: STRUCTURE, BONDING & ISOMERISM
**1. What is the hybridization of a carbon atom in a methane
(CH₄) molecule?**
A. sp
B. sp²
C. sp³
D. sp³d
**Correct answer:** sp³
**Rationale:** Carbon in CH₄ forms four single bonds (sigma
bonds) with hydrogen atoms. This requires four equivalent
hybrid orbitals, corresponding to sp³ hybridization. The
geometry is tetrahedral with bond angles of 109.5°. sp
hybridization occurs in alkynes (two bonds). sp² occurs in
alkenes (three bonds).
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---
**2. Which of the following best describes a covalent bond?**
A. Transfer of electrons from one atom to another
B. Sharing of electron pairs between atoms
C. Attraction between oppositely charged ions
D. Delocalization of electrons in a metal lattice
**Correct answer:** Sharing of electron pairs between atoms
**Rationale:** A covalent bond is formed when two atoms share
a pair of electrons. In organic chemistry, carbon forms covalent
bonds with other carbon atoms and with hydrogen, oxygen,
nitrogen, and halogens. Ionic bonds involve electron transfer.
Metallic bonds involve delocalized electrons.
---
**3. What is the molecular geometry of a carbon atom with sp²
hybridization?**
A. Linear
B. Trigonal planar
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C. Tetrahedral
D. Bent
**Correct answer:** Trigonal planar
**Rationale:** sp² hybridized carbon has three sigma bonds
arranged in a trigonal planar geometry with bond angles of
120°. The remaining unhybridized p orbital forms a pi bond. sp
hybridization gives linear geometry (180°). sp³ gives tetrahedral
(109.5°).
---
**4. Which of the following is an isomer of butane (C₄H₁₀)?**
A. 2-methylpropane
B. Propane
C. Pentane
D. Ethene
**Correct answer:** 2-methylpropane
**Rationale:** Isomers have the same molecular formula but
different structural arrangements. Butane (C₄H₁₀) has two
isomers: n-butane (straight chain) and 2-methylpropane
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(isobutane, branched). Propane (C₃H₈), pentane (C₅H₁₂), and
ethene (C₂H₄) have different molecular formulas.
---
**5. What is the difference between a sigma (σ) bond and a pi
(π) bond?**
A. Sigma bonds are weaker than pi bonds
B. Sigma bonds result from head-on overlap; pi bonds from
sideways overlap
C. Pi bonds allow free rotation; sigma bonds do not
D. Sigma bonds only occur in double bonds
**Correct answer:** Sigma bonds result from head-on overlap;
pi bonds from sideways overlap
**Rationale:** Sigma bonds form from head-on (end-to-end)
overlap of atomic orbitals and allow free rotation. Pi bonds form
from sideways overlap of p orbitals, are weaker than sigma
bonds, and restrict rotation. Single bonds are sigma; double
bonds have one sigma and one pi; triple bonds have one sigma
and two pi.
---
MIDTERM EXAM: ORGANIC
CHEMISTRY 2026/2027 QUESTIONS
WITH VERIFIED ANSWERS &
COMPLETE RATIONALES
## SECTION 1: STRUCTURE, BONDING & ISOMERISM
**1. What is the hybridization of a carbon atom in a methane
(CH₄) molecule?**
A. sp
B. sp²
C. sp³
D. sp³d
**Correct answer:** sp³
**Rationale:** Carbon in CH₄ forms four single bonds (sigma
bonds) with hydrogen atoms. This requires four equivalent
hybrid orbitals, corresponding to sp³ hybridization. The
geometry is tetrahedral with bond angles of 109.5°. sp
hybridization occurs in alkynes (two bonds). sp² occurs in
alkenes (three bonds).
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---
**2. Which of the following best describes a covalent bond?**
A. Transfer of electrons from one atom to another
B. Sharing of electron pairs between atoms
C. Attraction between oppositely charged ions
D. Delocalization of electrons in a metal lattice
**Correct answer:** Sharing of electron pairs between atoms
**Rationale:** A covalent bond is formed when two atoms share
a pair of electrons. In organic chemistry, carbon forms covalent
bonds with other carbon atoms and with hydrogen, oxygen,
nitrogen, and halogens. Ionic bonds involve electron transfer.
Metallic bonds involve delocalized electrons.
---
**3. What is the molecular geometry of a carbon atom with sp²
hybridization?**
A. Linear
B. Trigonal planar
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C. Tetrahedral
D. Bent
**Correct answer:** Trigonal planar
**Rationale:** sp² hybridized carbon has three sigma bonds
arranged in a trigonal planar geometry with bond angles of
120°. The remaining unhybridized p orbital forms a pi bond. sp
hybridization gives linear geometry (180°). sp³ gives tetrahedral
(109.5°).
---
**4. Which of the following is an isomer of butane (C₄H₁₀)?**
A. 2-methylpropane
B. Propane
C. Pentane
D. Ethene
**Correct answer:** 2-methylpropane
**Rationale:** Isomers have the same molecular formula but
different structural arrangements. Butane (C₄H₁₀) has two
isomers: n-butane (straight chain) and 2-methylpropane
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(isobutane, branched). Propane (C₃H₈), pentane (C₅H₁₂), and
ethene (C₂H₄) have different molecular formulas.
---
**5. What is the difference between a sigma (σ) bond and a pi
(π) bond?**
A. Sigma bonds are weaker than pi bonds
B. Sigma bonds result from head-on overlap; pi bonds from
sideways overlap
C. Pi bonds allow free rotation; sigma bonds do not
D. Sigma bonds only occur in double bonds
**Correct answer:** Sigma bonds result from head-on overlap;
pi bonds from sideways overlap
**Rationale:** Sigma bonds form from head-on (end-to-end)
overlap of atomic orbitals and allow free rotation. Pi bonds form
from sideways overlap of p orbitals, are weaker than sigma
bonds, and restrict rotation. Single bonds are sigma; double
bonds have one sigma and one pi; triple bonds have one sigma
and two pi.
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