The carbon-carbon double bond, denoted as C=C, is a fundamental structural feature in organic chemistry. It represents two covalent bonds between two carbon atoms, creating a double bond that is central to understanding concepts like degree of unsaturation and the infrared spectra of functional groups.
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The presence of a C=C bond increases the degree of unsaturation in a molecule, which is a key factor in calculating the number of rings and multiple bonds.
C=C bonds absorb infrared radiation at a characteristic frequency, allowing them to be identified in the IR spectra of organic compounds.
The presence and location of C=C bonds influence the overall reactivity and stability of organic molecules.
Conjugated C=C bonds, where double bonds are separated by single bonds, exhibit unique electronic properties and are commonly found in dyes, pigments, and certain pharmaceuticals.
The hybridization of carbon atoms involved in a C=C bond is $sp^2$, which gives the molecule a planar geometry and influences its physical and chemical properties.
Review Questions
Explain how the presence of a C=C bond affects the degree of unsaturation in a molecule.
The presence of a C=C bond increases the degree of unsaturation in a molecule. The degree of unsaturation is a measure of the number of rings and multiple bonds (double or triple bonds) in a molecule, and it is calculated using the formula: Degree of Unsaturation = (2C + 2 - H + N)/2, where C is the number of carbon atoms, H is the number of hydrogen atoms, and N is the number of nitrogen atoms. Each C=C bond contributes 1 to the degree of unsaturation, as it represents a multiple bond.
Describe how the C=C bond can be identified in the infrared (IR) spectrum of an organic compound.
The C=C bond has a characteristic absorption band in the infrared (IR) spectrum of organic compounds. Typically, the C=C bond absorbs IR radiation in the range of 1620-1680 cm$^{-1}$. This absorption is due to the stretching vibration of the carbon-carbon double bond. The presence and position of this absorption band in the IR spectrum can be used to identify the presence and location of C=C bonds in the structure of an organic molecule, which is a valuable tool in structural elucidation.
Analyze how the hybridization of carbon atoms involved in a C=C bond affects the geometry and reactivity of the molecule.
The carbon atoms involved in a C=C bond exhibit $sp^2$ hybridization, where each carbon atom has three $sp^2$ hybrid orbitals and one $p$ orbital. This $sp^2$ hybridization results in a planar geometry around the carbon atoms, with the bond angles being approximately 120 degrees. The presence of the $p$ orbitals perpendicular to the plane of the molecule allows for the formation of $ extbackslash pi$ bonds, which contribute to the overall stability and reactivity of the molecule. The planar geometry and the presence of $ extbackslash pi$ bonds influence the molecule's physical and chemical properties, such as its ability to participate in conjugation, undergo electrophilic addition reactions, and exhibit resonance stabilization.
Related terms
Alkene: An unsaturated hydrocarbon containing at least one carbon-carbon double bond.
Conjugation: The arrangement of multiple carbon-carbon double bonds or a combination of double and single bonds in an alternating pattern.
Hybridization: The mixing of atomic orbitals to form new hybrid orbitals, which determines the geometry and bonding properties of molecules.