Question

Indicate the hybridization expected at each carbon in the following: a. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\) b. \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\) c. \(\mathrm{HC} \equiv \mathrm{C}-\mathrm{CH}=\mathrm{O}\) d. \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{O}\) e. \(\mathrm{CH}_{2}=\mathrm{C}=\mathrm{CH}_{2}\)

Short answer

a: sp³, sp³, sp³; b: sp³, sp², sp²; c: sp, sp, sp²; d: sp³, sp²; e: sp², sp, sp².

Step-by-step solution

Analyze Structure a

For the molecule \( \text{CH}_{3}\text{CH}_{2}\text{CH}_{3} \) (propane), each carbon atom forms four single bonds. This means each carbon is \( \text{sp}^3 \) hybridized. Single bonded carbons form four \( \sigma \) bonds with 109.5° bond angles, typical of \( \text{sp}^3 \) hybridization.

Analyze Structure b

In \( \text{CH}_{3}\text{CH}=\text{CH}_{2} \) (propene), the first carbon attaches to three hydrogens and the next carbon. It forms four sigma bonds, indicating \( \text{sp}^3 \) hybridization. The second carbon is double-bonded to another carbon and single-bonded to the hydrogens, making it \( \text{sp}^2 \) hybridized. The third carbon, connected via the double bond and two hydrogens, is also \( \text{sp}^2 \) hybridized.

Analyze Structure c

For \( \text{HC} \equiv \text{C}-\text{CH}=\text{O} \) (propyne), the first carbon (\(\text{H}-\)) connected with a triple bond, is \( \text{sp} \) hybridized. Its \( \text{C} \equiv \text{C} \) carbon sharing two \( \pi \) bonds is \( \text{sp} \) as well. Moving to the \(-\text{CH}=\text{O}\) group, the \( -\text{CH}=\) group carbon is \( \text{sp}^2 \) because it forms a double bond.

Analyze Structure d

In \( \text{CH}_{3}-\text{CH}=\text{O} \) (acetaldehyde), the leftmost methyl \( \text{CH}_{3}- \) carbon uses \( \text{sp}^3 \) hybridization as it forms four single bonds. Whereas the \( -\text{CH}=\text{O} \) carbon, participating in a double bond, is \( \text{sp}^2 \) hybridized.

Analyze Structure e

For \( \text{CH}_{2}=\text{C}=\text{CH}_{2} \) (allene), both terminal \( \text{CH}_{2}= \) carbon atoms, with double bonds and single bonds, are \( \text{sp}^2 \) hybridized. The central \( =\text{C}= \) carbon aligns with linear geometry forming two \( \pi \) bonds perpendicular to each other, rendering it \( \text{sp} \) hybridized.

Key concepts

sp3 hybridization

In the world of carbon hybridization, an important concept is sp3 hybridization. This happens when one s-orbital combines with three p-orbitals in the carbon atom. The result is four equivalent sp3 hybrid orbitals. These orbitals arrange themselves in a tetrahedral geometry to minimize repulsion. This creates bond angles close to 109.5°. It is characteristic of carbon atoms that form four single bonds.

You'll most frequently see sp3 hybridization in alkanes, where each carbon is bonded to four other atoms. For instance, in propane (\( ext{CH}_3 ext{CH}_2 ext{CH}_3\)), every carbon forms four sigma (σ) bonds, which are single bonds. As these carbons share electrons with two neighboring carbon atoms and hydrogen atoms, they show sp3 hybridization.

• Stable due to even charge distribution.
• tetrahedral shape is the key identifier.
• Found in saturated hydrocarbons.

sp2 hybridization

A slightly different hybridization is sp2 hybridization. Here, one s-orbital mixes with two p-orbitals to form three sp2 hybrid orbitals. This leaves one p-orbital unhybridized. sp2 hybridized orbitals form a trigonal planar shape, resulting in 120° bond angles.

This hybridization is common in alkenes where double bonds are present. An example is propene (\( ext{CH}_3 ext{CH}= ext{CH}_2\)). In this case, carbon atoms involved in the double bond form one sigma bond and one pi (π) bond using the unhybridized p-orbital. This allows the double bond structure, while other bonds are formed by sp2 hybrid orbitals.

• Presence of double bonds indicates sp2 hybridization.
• Common in unsaturated hydrocarbons like alkenes.
• Flat planar due to its geometry.

sp hybridization

sp hybridization occurs when one s-orbital and one p-orbital merge to form two equivalent sp hybrid orbitals. This hybridization creates a linear geometry with 180° bond angles. The remaining two unhybridized p-orbitals are typically used to form pi bonds.

You'll find sp hybridization in carbon compounds with triple bonds or multiple double bonds. A classic example is propyne (\( ext{HC} riple \text{C}-\text{CH} = \text{O}\)). Here, the carbon atoms at the triple bond use sp hybridization to form one sigma bond and two pi bonds. The central atom in the allene molecule (\(\text{CH}_2=\text{C}=\text{CH}_2\)) is also sp hybridized. It forms two sp bonds arranged linearly, each perpendicular to a different plane.

• Indicated by linear structures and triple bonds.
• The molecule's linear shape distinguishes its hybridization.
• Optimal for compounds like alkynes and allene structures.