key term - C-H Bond

Definition

The C-H bond is a covalent bond formed between a carbon atom and a hydrogen atom. This bond is fundamental to organic chemistry and is present in a wide range of organic compounds, from simple alkanes to complex biomolecules. The C-H bond is crucial in understanding the structure, reactivity, and stability of organic molecules.

5 Must Know Facts For Your Next Test

1. In the context of sp3 hybridization, the C-H bond is formed by the overlap of a carbon's sp3 hybrid orbital and a hydrogen's 1s orbital, resulting in a tetrahedral arrangement of bonds around the carbon atom.
2. The bond dissociation energy of a C-H bond is relatively high, typically around 410 kJ/mol, making it a relatively stable and unreactive bond compared to other types of bonds in organic molecules.
3. The Hammond Postulate states that the transition state of a reaction resembles the structure of the reactants or products, depending on the relative energies of the reactants and products. This concept is important in understanding the reactivity of C-H bonds.
4. The acidity of alkynes, such as acetylene, is due to the ability of the terminal hydrogen atoms to be removed as protons, forming acetylide anions. This is a result of the high s-character of the C-H bonds in alkynes.
5. The E2 reaction, which involves the elimination of a leaving group and a hydrogen atom from adjacent carbon atoms, can be influenced by the strength of the C-H bond. The deuterium isotope effect, where the replacement of hydrogen with deuterium affects the reaction rate, is an important consideration in understanding the E2 mechanism.

Review Questions

• Explain the role of sp3 hybridization in the structure and properties of the C-H bond.
  • The C-H bond is formed by the overlap of a carbon's sp3 hybrid orbital and a hydrogen's 1s orbital. This sp3 hybridization results in a tetrahedral arrangement of bonds around the carbon atom, with the C-H bonds being directed towards the corners of the tetrahedron. The specific geometry and orbital overlap of the sp3 hybridized system contribute to the stability and reactivity of the C-H bond, as well as the overall structure and properties of organic molecules containing these bonds.
• Describe how bond dissociation energies and the Hammond Postulate relate to the reactivity of C-H bonds.
  • The relatively high bond dissociation energy of a C-H bond, typically around 410 kJ/mol, makes it a relatively stable and unreactive bond compared to other types of bonds in organic molecules. This stability is an important factor in understanding the reactivity of C-H bonds. The Hammond Postulate states that the transition state of a reaction resembles the structure of the reactants or products, depending on the relative energies of the reactants and products. This concept is crucial in predicting the reactivity of C-H bonds, as the transition state and the relative energies of the reactants and products can determine the ease with which the C-H bond can be broken or formed during a chemical reaction.
• Analyze the role of C-H bond acidity and the deuterium isotope effect in the E2 reaction mechanism.
  • The acidity of alkynes, such as acetylene, is due to the ability of the terminal hydrogen atoms to be removed as protons, forming acetylide anions. This is a result of the high s-character of the C-H bonds in alkynes, which increases the acidity of the hydrogen atoms. In the E2 reaction mechanism, the strength of the C-H bond can influence the reaction rate, as the elimination of a hydrogen atom is a key step. The deuterium isotope effect, where the replacement of hydrogen with deuterium affects the reaction rate, is an important consideration in understanding the E2 mechanism. The difference in bond strengths and vibrational frequencies between C-H and C-D bonds can lead to differences in the transition state energies, ultimately affecting the reaction kinetics and the overall mechanism.

Related terms

Hybridization:

The process of mixing atomic orbitals to form new, equivalent orbitals with specific geometries, which determines the shape and properties of molecules.

Bond Dissociation Energy:

The amount of energy required to break a specific chemical bond, which is an important factor in understanding the reactivity and stability of molecules.

Acidity:

The ability of a molecule or ion to donate a proton (H+) to another substance, which is influenced by the electronegativity and bond strengths within the molecule.