Question

Draw a line-bond structure for buta- 1,3 -diene, \(\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}_{2} ;\) indicate the hybridization of each carbon; and predict the value of each bond angle.

Short answer

All carbon atoms are \(sp^2\) hybridized with bond angles of \(120^\circ\).

Step-by-step solution

Identify the Formula and Structure

Buta-1,3-diene has the molecular formula \( ext{C}_4 ext{H}_6\). It contains a conjugated diene structure, with two double bonds between carbon atoms in a 1,3 arrangement.

Draw the Line-Bond Structure

Start by drawing a chain of four carbon atoms. Add double bonds between carbons 1 and 2, and between carbons 3 and 4. The structure looks like this: \( ext{H}_2 ext{C}= ext{CH}- ext{CH}= ext{CH}_2\).

Determine Hybridization of Each Carbon

1. Carbons 1 and 4 (\( ext{CH}_2\)): Each has a double bond and is bonded with two hydrogen atoms, indicating \(sp^2\) hybridization.2. Carbons 2 and 3 (\( ext{CH}\)): Each forms two carbon-carbon sigma bonds and one pi bond, indicating \(sp^2\) hybridization.

Predict Each Bond Angle

For \(sp^2\) hybridized atoms, bond angles are approximately \(120^\circ\). Thus, in buta-1,3-diene, the bond angles around each carbon atom will be approximately \(120^\circ\).

Key concepts

Buta-1,3-diene Structure and Characteristics

Buta-1,3-diene is an organic compound that is part of the alkene family, distinguished by its conjugated double bonds. Conjugated dienes have two double bonds separated by a single bond, creating a system that can delocalize electrons, granting extra stability.
The molecular formula for buta-1,3-diene is \( \mathrm{C}_4\mathrm{H}_6 \). In its line-bond structure, it is depicted as \( \mathrm{H}_2\mathrm{C}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}_2 \). This arrangement means that the double bonds are located between carbons 1 and 2, and carbons 3 and 4.

• Conjugated systems like these are crucial because they can engage in resonance, which affects the molecule's reactivity and stability.
• Buta-1,3-diene serves as an important building block in synthetic chemistry and is used in the production of polymers such as synthetic rubber.

Understanding Hybridization in Buta-1,3-diene

Hybridization is a concept in organic chemistry that explains the formation of equivalent orbitals through the mixing of atomic orbitals. In the case of buta-1,3-diene, each carbon atom involves \( sp^2 \) hybridization.
Certain characteristics define \( sp^2 \) hybridization:

• The \( sp^2 \) hybridization involves the mixing of one \(s\) orbital with two \(p\) orbitals.
• Each \( sp^2 \) hybridized carbon forms three sigma bonds. These can be a combination of carbon-hydrogen and carbon-carbon bonds.
• This allows each carbon to form a pi bond with an adjacent carbon by the lateral overlap of the unhybridized \(p\) orbital.

In buta-1,3-diene:

• Carbons in \( \mathrm{H}_2\mathrm{C}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}_2 \) use \( sp^2 \) hybridization to create strong bonding within the molecule.
• The delocalization of electrons among the \( \pi \) bonds provides extra stability, which is a feature of the conjugated double bonds.

Bond Angles in Buta-1,3-diene

The prediction of bond angles in organic molecules primarily relies on the concept of hybridization. As previously mentioned, buta-1,3-diene involves \( sp^2 \) hybridized carbon atoms.
Characteristics of \( sp^2 \) hybridization bond angles include:

• Each \( sp^2 \) hybridized carbon typically displays bond angles close to \( 120^\circ \).
• These angles result from the trigonal planar arrangement of orbitals, minimizing electron pair repulsion.

For buta-1,3-diene, this means:

• The carbon atoms form bond angles of approximately \( 120^\circ \) due to the \( sp^2 \) hybridization and planar geometry.
• This consistency in angle contributes to the planar and stable structure of the molecule.
• Such predictions align with the VSEPR theory, which suggests that molecules will adjust their shape to keep electron pairs as far apart as possible.

Understanding these geometric insights helps in predicting how buta-1,3-diene and similar conjugated systems behave in chemical reactions.