11.4 Carbon-carbon bond formation
8 min read•august 21, 2024
Carbon-carbon bond formation is the backbone of organic chemistry, shaping the structure and function of molecules. From single to triple bonds, these connections dictate molecular properties and reactivity, forming the basis for complex organic synthesis.
Understanding bond formation mechanisms like and is key to predicting and controlling reactions. Common reactions like and Diels-Alder enable the construction of intricate molecular frameworks, essential in synthesizing natural products and pharmaceuticals.
Types of carbon-carbon bonds
- Carbon-carbon bonds form the backbone of organic molecules, playing a crucial role in the structure and function of compounds
- Understanding different types of carbon-carbon bonds provides insight into molecular reactivity and properties in organic chemistry
Single vs double bonds
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- Single bonds (sigma bonds) consist of one shared electron pair between carbon atoms
- Double bonds comprise one sigma bond and one pi bond, resulting in stronger and shorter connections
- Single bonds allow free rotation, while double bonds restrict rotation due to the pi bond
- Bond strength increases from single to double bonds (C-C: 348 kJ/mol, C=C: 614 kJ/mol)
Triple bonds
- Triple bonds contain one sigma bond and two pi bonds between carbon atoms
- Exhibit the strongest and shortest carbon-carbon connections (C≡C: 839 kJ/mol)
- Linear geometry with 180° bond angles
- Highly reactive due to the electron-rich pi system
- Found in important compounds (acetylene)
Aromatic bonds
- Occur in cyclic, planar molecules with conjugated pi electrons
- Exhibit enhanced stability due to electron delocalization
- Follow Hückel's rule (4n+2 pi electrons)
- Resist addition reactions, favoring substitution reactions
- Found in many important biological molecules (nucleic acid bases)
Mechanisms of bond formation
- Carbon-carbon bond formation mechanisms are fundamental to organic synthesis
- Understanding these mechanisms allows chemists to predict and control reaction outcomes
Nucleophilic addition
- Involves the addition of a nucleophile to an electrophilic carbon
- Typically occurs with carbonyl compounds (, )
- Proceeds through a tetrahedral intermediate
- Results in the formation of a new carbon-carbon single bond
- Common in aldol reactions and Grignard additions
Electrophilic addition
- Involves the addition of an electrophile to a carbon-carbon multiple bond
- Follows Markovnikov's rule for unsymmetrical alkenes
- Proceeds through a carbocation intermediate
- Can lead to the formation of new carbon-carbon single bonds
- Observed in alkene halogenation and hydration reactions
Radical reactions
- Involve the formation and reaction of radical species
- Proceed through initiation, propagation, and termination steps
- Can form carbon-carbon bonds through radical coupling or addition
- Often initiated by heat, light, or radical initiators
- Used in polymerization reactions and some organic syntheses
Pericyclic reactions
- Involve the concerted reorganization of electrons in cyclic transitions states
- Include cycloadditions, electrocyclic reactions, and sigmatropic rearrangements
- Follow the Woodward-Hoffmann rules for orbital symmetry
- Can form multiple carbon-carbon bonds in a single step
- Exemplified by the and electrocyclic ring closures
Common carbon-carbon reactions
- Carbon-carbon bond-forming reactions are essential tools in organic synthesis
- These reactions allow for the construction of complex molecular frameworks
Aldol condensation
- Involves the reaction of two carbonyl compounds to form a β-hydroxy carbonyl
- Proceeds through enolate formation and nucleophilic addition
- Can be followed by dehydration to form an α,β-unsaturated carbonyl
- Useful for creating carbon-carbon bonds and extending carbon chains
- Employed in the synthesis of many natural products and pharmaceuticals
Diels-Alder reaction
- Cycloaddition reaction between a conjugated diene and a dienophile
- Forms two new carbon-carbon single bonds in a single step
- Produces a cyclohexene ring system with high
- Follows concerted mechanism with suprafacial approach
- Widely used in the synthesis of complex cyclic compounds
Grignard reaction
- Utilizes organomagnesium halides (Grignard reagents) as nucleophiles
- Forms carbon-carbon bonds by adding to carbonyl compounds
- Produces alcohols upon workup with aqueous acid
- Highly versatile due to the variety of available Grignard reagents
- Used in the synthesis of alcohols, carboxylic acids, and ketones
Wittig reaction
- Converts aldehydes or ketones into alkenes using phosphonium ylides
- Forms carbon-carbon double bonds with defined geometry (E or Z)
- Proceeds through a four-membered oxaphosphetane intermediate
- Widely used in the synthesis of complex alkenes and natural products
- Allows for the selective formation of trisubstituted and tetrasubstituted alkenes
Catalysts for bond formation
- Catalysts play a crucial role in facilitating carbon-carbon bond formation
- They can improve reaction efficiency, selectivity, and sustainability
Transition metal catalysts
- Utilize d-block elements to catalyze various organic transformations
- Include palladium, ruthenium, rhodium, and nickel catalysts
- Enable (Suzuki, Heck, Sonogashira)
- Facilitate olefin metathesis and hydroformylation reactions
- Often operate through oxidative addition and reductive elimination steps
Organocatalysts
- Small organic molecules that catalyze reactions without metal centers
- Include proline derivatives, cinchona alkaloids, and thioureas
- Promote enantioselective transformations through hydrogen bonding or covalent interactions
- Used in asymmetric aldol reactions and Michael additions
- Offer advantages of low toxicity and tolerance to air and moisture
Enzyme catalysis
- Utilizes biological catalysts to promote carbon-carbon bond formation
- Includes aldolases, transketolases, and polyketide synthases
- Offers high selectivity and efficiency under mild conditions
- Operates through specific active site interactions and transition state stabilization
- Employed in biocatalysis for pharmaceutical and fine chemical synthesis
Stereochemistry in bond formation
- Stereochemistry plays a crucial role in determining the properties and functions of organic molecules
- Control of stereochemistry is essential in the synthesis of pharmaceuticals and natural products
Stereospecific reactions
- Produce a single stereoisomer from a single stereoisomeric starting material
- Maintain the stereochemical information throughout the reaction
- Include SN2 reactions and syn eliminations
- Rely on the principle of least motion and orbital overlap
- Useful for retaining or inverting existing stereocenters
Stereoselective reactions
- Preferentially form one stereoisomer over others when multiple are possible
- Include diastereoselective and enantioselective reactions
- Often controlled by steric factors or chiral catalysts/auxiliaries
- Exemplified by asymmetric hydrogenations and aldol reactions
- Critical in the synthesis of enantiomerically pure compounds
Asymmetric synthesis
- Involves the creation of new stereocenters with preferential formation of one enantiomer
- Utilizes chiral catalysts, auxiliaries, or starting materials
- Includes asymmetric hydrogenation, epoxidation, and Diels-Alder reactions
- Measures effectiveness using enantiomeric excess (ee)
- Essential in the pharmaceutical industry for producing single-enantiomer drugs
Synthetic applications
- Carbon-carbon bond formation is fundamental to the synthesis of complex organic molecules
- These techniques enable the construction of diverse molecular architectures
Total synthesis
- Involves the complete chemical synthesis of complex organic molecules
- Requires strategic planning and sequencing of multiple reactions
- Often targets natural products or pharmaceutically active compounds
- Demonstrates the power and limitations of synthetic methodologies
- Exemplified by Woodward's synthesis of strychnine and Corey's synthesis of prostaglandins
Natural product synthesis
- Focuses on recreating molecules produced by living organisms
- Involves complex, multi-step sequences to build intricate structures
- Often requires development of new synthetic methodologies
- Provides access to scarce compounds for biological testing
- Includes synthesis of terpenes, alkaloids, and polyketides
Polymer synthesis
- Utilizes carbon-carbon bond formation to create large macromolecules
- Includes chain-growth and step-growth polymerization mechanisms
- Produces materials with diverse properties (plastics, fibers, rubbers)
- Employs techniques (free radical, ionic, coordination polymerization)
- Enables the development of advanced materials for various applications
Analytical techniques
- Analytical techniques are essential for characterizing and confirming the structure of organic compounds
- These methods provide crucial information about carbon-carbon bonds and molecular structure
NMR spectroscopy
- Provides detailed information about molecular structure and carbon environments
- Utilizes 1H and 13C NMR to analyze hydrogen and carbon atoms
- Reveals information about bond types, connectivity, and stereochemistry
- Employs chemical shifts, coupling constants, and multiplicity patterns
- Essential for structure elucidation of complex organic molecules
Mass spectrometry
- Determines the molecular mass and fragmentation patterns of compounds
- Provides information about molecular formula and structural features
- Utilizes various ionization techniques (EI, ESI, MALDI)
- Enables high-resolution mass determination for accurate formula assignment
- Crucial for analyzing reaction products and identifying unknown compounds
X-ray crystallography
- Determines the three-dimensional structure of crystalline compounds
- Provides precise information about bond lengths, angles, and stereochemistry
- Requires single crystals of suitable quality for analysis
- Utilizes X-ray diffraction patterns to reconstruct electron density maps
- Essential for confirming the absolute configuration of chiral molecules
Environmental considerations
- Green chemistry principles are increasingly important in organic synthesis
- Sustainable approaches to carbon-carbon bond formation minimize environmental impact
Green chemistry approaches
- Emphasizes the design of chemical processes that reduce or eliminate hazardous substances
- Utilizes renewable feedstocks and biodegradable reagents when possible
- Focuses on energy efficiency and waste reduction in synthetic processes
- Employs alternative reaction media (water, ionic liquids, supercritical CO2)
- Aims to develop safer and more sustainable synthetic methodologies
Atom economy
- Measures the efficiency of chemical reactions in terms of atoms utilized
- Calculates the percentage of atoms from reactants incorporated into the desired product
- Encourages the development of reactions with minimal byproduct formation
- Favors addition reactions over substitution or elimination processes
- Promotes the use of catalytic over stoichiometric reagents
Sustainable bond formation
- Focuses on developing environmentally friendly carbon-carbon bond-forming reactions
- Utilizes renewable resources and bio-based starting materials
- Employs catalytic processes to minimize waste and improve efficiency
- Explores photochemical and electrochemical methods for bond formation
- Aims to reduce the use of toxic reagents and solvents in organic synthesis
Industrial processes
- Carbon-carbon bond formation is crucial in various industrial sectors
- These processes enable the large-scale production of important chemicals and materials
Petroleum chemistry
- Involves the transformation of hydrocarbons from crude oil into valuable products
- Utilizes cracking and reforming processes to create carbon-carbon bonds
- Produces important feedstocks for the chemical industry (ethylene, propylene)
- Employs catalytic processes for improved selectivity and efficiency
- Faces challenges in developing more sustainable and environmentally friendly processes
Pharmaceutical synthesis
- Focuses on the large-scale production of drug molecules
- Requires efficient and scalable carbon-carbon bond-forming reactions
- Emphasizes stereoselective processes for single-enantiomer drug synthesis
- Utilizes flow chemistry and continuous processes for improved efficiency
- Faces stringent regulatory requirements for purity and quality control
Materials science applications
- Employs carbon-carbon bond formation in the synthesis of advanced materials
- Includes the production of polymers, carbon fibers, and nanostructures
- Utilizes cross-coupling reactions for the synthesis of conjugated materials
- Develops new materials with tailored electronic and mechanical properties
- Explores sustainable alternatives to petroleum-based materials
Key Terms to Review (20)
Aldehydes: Aldehydes are organic compounds containing a carbonyl group (C=O) where the carbon is bonded to at least one hydrogen atom, making them distinct from ketones. This unique structure allows aldehydes to participate in various chemical reactions, particularly those involving nucleophiles, making them important intermediates in organic synthesis and a key feature in many biochemical processes.
Aldol Condensation: Aldol condensation is a reaction between aldehydes or ketones containing a β-hydrogen that leads to the formation of β-hydroxy aldehydes or ketones, which can further dehydrate to yield enones or α,β-unsaturated carbonyl compounds. This reaction not only builds new carbon-carbon bonds but also utilizes enolate ions formed from the starting carbonyl compounds, highlighting its role in complex organic synthesis.
Alkyl halide: An alkyl halide is a type of organic compound formed by substituting one or more hydrogen atoms in an alkane with halogen atoms (fluorine, chlorine, bromine, or iodine). These compounds are important in organic synthesis as they can undergo various reactions to form amines or facilitate carbon-carbon bond formation, which are essential in building larger, more complex molecules.
Carbonyl group: A carbonyl group is a functional group characterized by a carbon atom double-bonded to an oxygen atom, represented as C=O. This structure is crucial in organic chemistry as it forms the backbone of many important compounds, including aldehydes, ketones, and carboxylic acids, and plays a significant role in various chemical reactions and spectroscopic analyses.
Cross-coupling reactions: Cross-coupling reactions are chemical reactions that allow for the formation of carbon-carbon bonds by coupling two different carbon-containing fragments in the presence of a transition metal catalyst. These reactions are significant in organic synthesis as they provide a strategic way to construct complex molecules with specific structural features, enhancing the ability to design and create diverse compounds.
Diastereomers: Diastereomers are stereoisomers that are not related as mirror images. This means they have multiple chiral centers and differ at one or more of those centers, leading to different physical and chemical properties. Understanding diastereomers is crucial in organic chemistry, especially when discussing reactions involving carbon-carbon bond formation, where the stereochemistry can significantly influence the outcome and selectivity of reactions.
Diels-Alder Reaction: The Diels-Alder reaction is a cycloaddition reaction between a diene and a dienophile that results in the formation of a six-membered ring. This reaction is significant in organic synthesis as it allows for the construction of complex cyclic structures in a single step, highlighting its utility in creating polycyclic aromatic hydrocarbons and facilitating carbon-carbon bond formation.
Electrophilic Addition: Electrophilic addition is a fundamental reaction mechanism where an electrophile reacts with a nucleophile, resulting in the formation of a new covalent bond. This process is crucial in organic chemistry as it allows for the transformation of unsaturated compounds, such as alkenes and alkynes, into more complex molecules. By facilitating the addition of various groups to carbonyls and other reactive sites, electrophilic addition plays a vital role in synthesizing diverse organic compounds.
Grignard reaction: The Grignard reaction is a powerful organic reaction that involves the formation of carbon-carbon bonds through the reaction of Grignard reagents with electrophiles. This reaction is crucial for synthesizing various organic compounds and allows for functional group interconversions, particularly involving aldehydes and ketones, by forming new carbon chains.
Henry Gilman: Henry Gilman was a prominent chemist known for his contributions to organic chemistry, particularly in the development of methods for synthesizing carbon-carbon bonds and studying organocopper reagents. His work laid the foundation for key techniques in organic synthesis, influencing how enolates can be alkylated and enhancing our understanding of reaction mechanisms in forming complex molecules.
Ketones: Ketones are organic compounds characterized by a carbonyl group (C=O) bonded to two carbon atoms. They play a crucial role in various chemical reactions and processes, often serving as key intermediates in synthesis and transformations involving carbonyl compounds.
Michael Addition: Michael addition is a type of nucleophilic addition reaction where a nucleophile adds to an α,β-unsaturated carbonyl compound. This reaction involves the formation of a new carbon-carbon bond and typically occurs under basic conditions, making it an important strategy in organic synthesis to build larger molecules from smaller ones.
Nucleophilic Addition: Nucleophilic addition is a chemical reaction where a nucleophile forms a bond with an electrophilic center, typically in carbonyl compounds like aldehydes and ketones. This process is central to many organic reactions, leading to the formation of alcohols and larger molecules through the addition of various nucleophiles to carbonyl carbons.
Pericyclic reactions: Pericyclic reactions are a unique class of organic reactions characterized by the simultaneous breaking and forming of bonds in a cyclic transition state. These reactions often involve the rearrangement of electrons in a concerted manner, meaning that the process occurs in one step without intermediates, and they typically involve systems with cyclic π-bonds. Understanding the behavior of these reactions is crucial for predicting product formation and reactivity, as well as for utilizing Woodward-Hoffmann rules to determine allowed and forbidden pathways in complex transformations, including carbon-carbon bond formation.
R. D. Haworth: R. D. Haworth was a prominent British chemist known for his significant contributions to carbohydrate chemistry and the development of the Haworth projection, a way to represent cyclic sugars. His work laid the foundation for understanding the structure and reactivity of monosaccharides and polysaccharides, which are crucial in organic chemistry and biochemistry.
Radical Reactions: Radical reactions are chemical processes involving reactive species known as radicals, which are molecules or atoms that have unpaired electrons. These reactions play a significant role in organic chemistry, particularly in carbon-carbon bond formation, where radicals can initiate new bond creation through their highly reactive nature. The ability of radicals to donate or accept electrons allows them to participate in various reaction mechanisms, such as chain reactions and substitution reactions.
Solvent polarity: Solvent polarity refers to the ability of a solvent to dissolve polar or ionic substances, determined by its molecular structure and the distribution of electric charge. A polar solvent has a significant difference in electronegativity between its constituent atoms, leading to a dipole moment, which enhances its ability to solvate ions and polar molecules. Understanding solvent polarity is essential for predicting the outcomes of reactions, especially in carbon-carbon bond formation, where the choice of solvent can influence reaction rates and mechanisms.
Stereoselectivity: Stereoselectivity is the preference of a chemical reaction to produce one stereoisomer over another when multiple stereoisomers are possible. This property is crucial in organic chemistry as it directly influences the biological activity and properties of the compounds formed, making it vital for the development of pharmaceuticals and other chemical products.
Temperature effect: The temperature effect refers to how the temperature of a reaction influences the rate at which reactants combine to form products, particularly in carbon-carbon bond formation reactions. In organic chemistry, this is crucial as temperature can alter the stability of intermediates, affect the kinetics of bond formation, and ultimately influence the yield of desired products. Understanding the temperature effect is vital for optimizing reaction conditions in synthetic strategies.
Wittig Reaction: The Wittig reaction is a chemical reaction that enables the formation of alkenes through the reaction of an aldehyde or ketone with a phosphonium ylide. This process is significant for carbon-carbon bond formation, allowing chemists to synthesize complex organic molecules with high specificity and yield. The reaction exemplifies a powerful method for creating double bonds between carbon atoms, which is crucial in various organic synthesis applications.