20.1 Hydrocarbons
3 min read•june 25, 2024
are the simplest , made of just carbon and hydrogen. They're everywhere in nature and are used to make fuels, plastics, and medicines. These versatile molecules can form different shapes and structures, giving them unique properties.
Naming hydrocarbons follows specific rules based on their structure. have only single bonds, while and have double or triple bonds. The number of carbon atoms and bond types determine their names and formulas.
Introduction to Hydrocarbons
Significance of hydrocarbons
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- Compounds composed of only carbon and hydrogen atoms form the simplest organic compounds and serve as building blocks for more complex organic molecules
- Abundant in nature with diverse applications including main components of fossil fuels (natural gas, petroleum, coal) and used in production of plastics, pharmaceuticals, and other synthetic materials
- Exhibit wide range of structural diversity by forming linear, branched, or cyclic structures with single, double, or triple bonds between carbon atoms contributing to varied physical and chemical properties
IUPAC nomenclature for hydrocarbons
- (alkanes) contain only single bonds between carbon atoms following general formula where represents number of carbon atoms
- naming: Use prefix corresponding to number of carbon atoms followed by "-ane" ( , , )
- Unsaturated hydrocarbons contain at least one double or triple bond between carbon atoms
- have one or more double bonds with general formula
- IUPAC naming: Use prefix corresponding to number of carbon atoms followed by "-ene" ( , )
- Multiple double bonds use suffix "-diene", "-triene", etc.
- have one or more triple bonds with general formula
- IUPAC naming: Use prefix corresponding to number of carbon atoms followed by "-yne" ( , )
- Multiple triple bonds use suffix "-diyne", "-triyne", etc.
- have one or more double bonds with general formula
Reactions and Isomerism
Reactions of alkanes vs alkenes
- Alkanes relatively unreactive due to strength and stability of C-C and C-H single bonds ()
- Undergo reactions with oxygen producing carbon dioxide and water
- Can also undergo reactions with halogens in presence of light or heat
- Alkenes more reactive than alkanes due to presence of C=C double bond
- Undergo addition reactions where atoms or molecules add across the double bond
- : addition of
- : addition of
- : addition of
- Can also undergo reactions forming long-chain molecules
- Undergo addition reactions where atoms or molecules add across the double bond
- Alkynes also more reactive than alkanes due to presence of C≡C triple bond
- Undergo similar addition reactions as alkenes but often occur in two steps due to triple bond
- Can also undergo to form alkenes or alkanes depending on reaction conditions
Isomers in hydrocarbon molecules
- are compounds with same molecular formula but different arrangements of atoms
- have same molecular formula but differ in connectivity of atoms
- Butane () has two : (straight-chain) and (branched)
- have same molecular formula and connectivity but differ in spatial arrangement of atoms occurring in compounds with double bonds or cyclic structures
- : Atoms or groups can be on same side (cis) or opposite sides (trans) of a double bond
- 2-butene () has two geometric isomers, and
- : Atoms or groups can rotate around single bonds resulting in different conformations
- () can exist in chair or boat conformations
- : Atoms or groups can be on same side (cis) or opposite sides (trans) of a double bond
Structural Features and Properties
Hybridization and bonding
- Carbon atoms in hydrocarbons undergo , which affects their bonding properties
- sp³ hybridization in alkanes results in tetrahedral geometry
- sp² hybridization in alkenes leads to trigonal planar geometry around double bonds
- sp hybridization in alkynes creates linear geometry around triple bonds
Functional groups and reactivity
- are specific arrangements of atoms within molecules that give them characteristic chemical properties
- In hydrocarbons, the presence of double or triple bonds acts as a , increasing reactivity
Aromaticity and stability
- Aromatic compounds, such as benzene, exhibit special stability due to delocalized electrons
- is characterized by a planar ring structure with conjugated double bonds and follows Hückel's rule
Saturation and physical properties
- Saturated hydrocarbons (alkanes) have all single bonds between carbon atoms
- Unsaturated hydrocarbons (alkenes and alkynes) contain at least one double or triple bond
- The degree of saturation affects physical properties such as boiling point and reactivity
Key Terms to Review (61)
Addition reaction: An addition reaction is a chemical reaction where atoms or groups are added to a double or triple bond in an organic molecule, resulting in the saturation of the bond. These reactions are typical in alkenes and alkynes.
Alkanes: Alkanes are a class of saturated hydrocarbons, meaning they consist entirely of carbon and hydrogen atoms with single covalent bonds. They are the simplest and most stable organic compounds, characterized by their straight or branched carbon chains and the absence of double or triple bonds.
Alkenes: Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). They are unsaturated compounds with the general formula $C_nH_{2n}$.
Alkenes: Alkenes are a class of unsaturated hydrocarbons that contain at least one carbon-carbon double bond. They are characterized by the presence of this reactive double bond, which gives them unique chemical properties and reactivity compared to alkanes.
Alkyl group: An alkyl group is a functional group derived from alkanes by removing one hydrogen atom. It is often represented by the symbol R in chemical structures.
Alkynes: Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. They have the general formula $C_nH_{2n-2}$.
Alkynes: Alkynes are a class of unsaturated hydrocarbons that contain a carbon-carbon triple bond. They are the second simplest type of hydrocarbons after alkanes and have the general formula C_nH_(2n-2), where n represents the number of carbon atoms in the molecule.
Aromatic hydrocarbons: Aromatic hydrocarbons are a class of hydrocarbons that contain one or more benzene rings in their molecular structure. They are known for their stability and unique chemical properties due to resonance.
Aromaticity: Aromaticity is a chemical property that describes the stabilizing effect of cyclic, planar, and conjugated molecular structures. It is a crucial concept in organic chemistry, particularly in understanding the behavior and reactivity of certain hydrocarbon compounds.
C2H2: C2H2, also known as acetylene, is a simple hydrocarbon compound composed of two carbon atoms and two hydrogen atoms. It is a colorless, flammable gas that is widely used in various industrial and chemical applications.
C2H4: C2H4, commonly known as ethylene, is a colorless gas with a sweet odor that is a key hydrocarbon compound. It is an unsaturated hydrocarbon, meaning it contains at least one double bond between carbon atoms. Ethylene plays a vital role in the production of plastics and serves as a plant hormone, influencing growth and ripening processes.
C2H6: C2H6, also known as ethane, is a simple hydrocarbon compound composed of two carbon atoms and six hydrogen atoms. It is a key component in the study of hydrocarbons, which are organic compounds consisting solely of carbon and hydrogen atoms.
C3H4: C3H4 is the molecular formula representing a hydrocarbon compound consisting of three carbon atoms and four hydrogen atoms. This formula indicates that it belongs to the class of hydrocarbons, specifically alkenes or alkynes, depending on the bonding between the carbon atoms. Understanding C3H4 helps in studying the properties, structures, and reactions of hydrocarbons, which are fundamental to organic chemistry.
C3H6: C3H6 is a chemical formula that represents a simple hydrocarbon molecule with three carbon atoms and six hydrogen atoms. This molecular formula is commonly associated with the organic compound propene, which is an important industrial chemical and a key building block for many other organic compounds.
C3H8: C3H8, also known as propane, is a simple hydrocarbon with the molecular formula C3H8. It is a colorless, odorless gas that is commonly used as a fuel source and in various industrial applications.
C4H10: C4H10 is the chemical formula for butane, a simple alkane hydrocarbon with four carbon atoms and ten hydrogen atoms. Hydrocarbons are organic compounds composed solely of carbon and hydrogen atoms, and they are the simplest organic molecules.
C4H8: C4H8 is a chemical formula that represents a class of organic compounds known as alkenes, which are characterized by the presence of a carbon-carbon double bond. These compounds are important in the field of hydrocarbons, as they are derived from the basic building blocks of organic chemistry and play a significant role in various chemical processes and applications.
C6H12: C6H12 is a chemical formula that represents a hydrocarbon compound with the molecular formula of six carbon atoms and twelve hydrogen atoms. Hydrocarbons are organic compounds composed solely of carbon and hydrogen atoms, and they are the simplest organic compounds.
Carbon-carbon bonds: Carbon-carbon bonds are the connections between carbon atoms in organic molecules, crucial for the structure and stability of hydrocarbons. These bonds can vary in type, including single, double, and triple bonds, influencing the chemical properties and reactivity of the molecules they form. Understanding carbon-carbon bonds is essential for grasping the behavior of hydrocarbons, which are the foundational compounds in organic chemistry.
CH4: CH4, also known as methane, is the simplest alkane hydrocarbon with a chemical formula consisting of one carbon atom and four hydrogen atoms. It is a colorless, odorless, and flammable gas that plays a crucial role in the context of molecular structure, polarity, and hydrocarbon chemistry.
Cis-2-butene: Cis-2-butene is a type of alkene, a hydrocarbon with a carbon-carbon double bond. It is a structural isomer of trans-2-butene, differing in the orientation of the substituents around the double bond.
Cis-Trans Isomerism: Cis-trans isomerism is a type of stereoisomerism in organic chemistry where two molecules have the same molecular formula and connectivity, but differ in the spatial arrangement of their atoms. This isomerism occurs when there is a carbon-carbon double bond or a ring structure that restricts rotation, leading to different orientations of substituents on either side of the double bond or ring.
CnH2n: CnH2n is a general formula that represents a class of organic compounds known as alkenes, which are unsaturated hydrocarbons. The 'n' in the formula represents the number of carbon atoms, and the '2n' represents the number of hydrogen atoms in the molecule.
CnH2n-2: CnH2n-2 is a general formula that represents a class of unsaturated hydrocarbons, specifically alkenes, where 'n' represents the number of carbon atoms in the molecule. These hydrocarbons have a double bond between two carbon atoms, resulting in a lower hydrogen-to-carbon ratio compared to saturated hydrocarbons.
CnH2n+2: CnH2n+2 is a general chemical formula that represents a class of organic compounds known as alkanes, which are saturated hydrocarbons. The formula indicates that the compound has a carbon chain with n number of carbon atoms, and the number of hydrogen atoms is always 2n plus 2.
Combustion: Combustion is a chemical reaction that occurs when a fuel, such as a hydrocarbon, reacts with an oxidizing agent, typically oxygen, to release energy in the form of heat and light. This exothermic reaction is a fundamental process in the understanding of chemistry, particularly in the context of stoichiometry, the occurrence and preparation of oxygen, and the properties of hydrocarbons.
Combustion analysis: Combustion analysis is a method used to determine the elemental composition, especially carbon and hydrogen, of an organic compound by burning the sample and analyzing the resulting products. This technique is essential for quantitative chemical analysis.
Conformational Isomerism: Conformational isomerism is a type of stereoisomerism where molecules can exist in different spatial arrangements, or conformations, without breaking any covalent bonds. These conformations are in dynamic equilibrium and can interconvert through the rotation of single bonds.
Coordination isomers: Coordination isomers are a type of structural isomerism in coordination compounds where the composition of the complex ions varies but the overall formula remains the same. These arise when ligands and counterions exchange places between coordination spheres.
Cyclohexane: Cyclohexane is a cyclic hydrocarbon compound with the chemical formula C₆H₁₂. It is a colorless, flammable liquid that is widely used as a solvent and in the production of various chemicals.
Ethane: Ethane is a simple alkane hydrocarbon with the chemical formula C2H6. It is a colorless, odorless, and flammable gas that is the second member of the alkane series and plays an important role in the context of the topics 'Occurrence, Preparation, and Compounds of Hydrogen' and 'Hydrocarbons'.
Ethene: Ethene, also known as ethylene, is a simple unsaturated hydrocarbon with the molecular formula C2H4. It is a colorless, flammable gas that is widely used in the chemical industry and is a key intermediate in the production of many organic compounds.
Ethyne: Ethyne, also known as acetylene, is a simple hydrocarbon with the chemical formula C$_2$H$_2$. It is a colorless, flammable gas with a distinctive odor and is widely used in various industrial and commercial applications.
Functional group: A functional group is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule. Functional groups are the sites of reactivity in organic compounds.
Functional Groups: Functional groups are specific arrangements of atoms within organic molecules that determine the chemical reactivity and properties of those molecules. They are the key to understanding the behavior and classification of various organic compounds.
Geometric Isomers: Geometric isomers, also known as cis-trans isomers, are a type of stereoisomers that arise when molecules have restricted rotation around a carbon-carbon double bond. These isomers have the same molecular formula and connectivity but differ in the spatial arrangement of their atoms, leading to distinct physical and chemical properties.
Halogenation: Halogenation is a chemical reaction that involves the addition of halogens, such as fluorine, chlorine, bromine, or iodine, to a compound, typically an organic molecule. This process can modify the physical and chemical properties of the compound, often increasing its reactivity. Halogenation is crucial in various applications, including the synthesis of organic compounds and in the transformation of hydrocarbons.
Hybridization: Hybridization is the concept in chemistry where atomic orbitals combine to form new hybrid orbitals that are suitable for the pairing of electrons to form chemical bonds. This idea helps explain molecular geometry and bonding properties, linking the arrangement of atoms in a molecule to their electron configurations and the types of bonds formed.
Hydration: Hydration refers to the process of adding water or other liquid to a substance, resulting in the formation of a hydrated compound or solution. This term is particularly relevant in the context of dissolution, electrolytes, and hydrocarbon chemistry.
Hydrocarbons: Hydrocarbons are organic compounds consisting entirely of carbon and hydrogen atoms. They are the simplest organic compounds and serve as the building blocks for more complex organic molecules. Hydrocarbons are of great importance in the context of both the occurrence and preparation of hydrogen compounds, as well as being a fundamental class of organic compounds.
Hydrogenation: Hydrogenation is a chemical reaction that involves the addition of hydrogen (H$_2$) to another compound, typically in the presence of a catalyst. It is commonly used to convert unsaturated fats to saturated fats and in the production of various chemicals.
Hydrogenation: Hydrogenation is a chemical process that involves the addition of hydrogen gas to unsaturated organic compounds, such as alkenes and alkynes, in the presence of a catalyst. This process results in the conversion of the unsaturated compounds into their corresponding saturated compounds, which have important applications in various industries.
Isobutane: Isobutane, also known as 2-methylpropane, is a branched-chain alkane hydrocarbon with the chemical formula C4H10. It is an isomer of butane, a common fuel gas, and has a wide range of applications in the chemical industry and as a refrigerant.
Isomers: Isomers are chemical compounds that have the same molecular formula, meaning they are composed of the same types and numbers of atoms, but have different arrangements or structures. This concept is crucial in understanding the properties and behavior of organic compounds, particularly in the context of chemical formulas and hydrocarbon structures.
IUPAC: IUPAC, or the International Union of Pure and Applied Chemistry, is the recognized authority for establishing standardized rules and guidelines for the naming and representation of chemical compounds. It serves as the global organization responsible for developing a systematic and unambiguous system of chemical nomenclature that facilitates clear communication among chemists worldwide.
Methane: Methane is a colorless, odorless gas with the chemical formula CH₄, primarily composed of carbon and hydrogen. It is the simplest alkane and serves as a primary component of natural gas, making it an important fuel source and a significant greenhouse gas contributing to climate change.
N-Butane: n-Butane is a straight-chain, saturated hydrocarbon with the chemical formula C4H10. It is a colorless, odorless gas that is the second-simplest alkane after methane, and is commonly used as a fuel and refrigerant.
Organic compounds: Organic compounds are chemical compounds that contain carbon atoms bonded to hydrogen, oxygen, or other carbon atoms. They form the basis of all known life and include a vast array of substances including hydrocarbons.
Polymerization: Polymerization is the process of combining many small, repeating molecular units called monomers to form larger, more complex molecules known as polymers. This process is essential in the formation of various natural and synthetic materials, including plastics, rubbers, and proteins.
Propane: Propane is a colorless, odorless, flammable gas that is a member of the alkane family of hydrocarbons. It is commonly used as a fuel for heating, cooking, and powering various appliances, and is also an important industrial chemical with numerous applications in the context of the topics 18.5 Occurrence, Preparation, and Compounds of Hydrogen and 20.1 Hydrocarbons.
Propene: Propene, also known as propylene, is a colorless, flammable gas that is an important organic compound and a member of the alkene family of hydrocarbons. It is a key intermediate in the petrochemical industry and is used in the production of a wide range of products, including plastics, resins, and fuels.
Propyne: Propyne, also known as methylacetylene, is a simple hydrocarbon with the chemical formula C₃H₄. It is a colorless, flammable gas that is the simplest alkyne, a class of unsaturated hydrocarbons characterized by a carbon-carbon triple bond.
Saturated hydrocarbons: Saturated hydrocarbons are organic compounds consisting entirely of single bonds between carbon atoms and are fully 'saturated' with hydrogen atoms. They are also known as alkanes.
Saturated vs. Unsaturated: Saturation refers to the number of hydrogen atoms bonded to the carbon atoms in a hydrocarbon molecule. Saturated hydrocarbons have the maximum number of hydrogen atoms, while unsaturated hydrocarbons have fewer hydrogen atoms and contain one or more double or triple bonds between carbon atoms.
Skeletal structure: A skeletal structure is a simplified representation of an organic molecule that shows the bonding between atoms, excluding hydrogen atoms. It uses lines to represent carbon-carbon bonds and vertices or line ends to represent carbon atoms.
Structural isomers: Structural isomers are compounds with the same molecular formula but different structural arrangements of atoms. These differences can result in distinct physical and chemical properties.
Structural Isomers: Structural isomers are compounds that have the same molecular formula but different arrangements of atoms in space, resulting in distinct chemical and physical properties. This concept is particularly important in the context of chemical formulas and hydrocarbon compounds.
Substituents: Substituents are atoms or groups of atoms that replace hydrogen atoms on the parent hydrocarbon chain. They play a key role in determining the properties and reactivity of organic molecules.
Substitution: Substitution is a fundamental chemical reaction in which one or more atoms or functional groups in a molecule are replaced by different atoms or functional groups, resulting in the formation of a new compound with altered properties.
Substitution reaction: A substitution reaction is a chemical reaction where an atom or group of atoms in a molecule is replaced by another atom or group of atoms. It is common in organic chemistry, especially involving halogenated compounds.
Trans-2-butene: trans-2-butene is a type of alkene, a hydrocarbon with a carbon-carbon double bond. It is a geometric isomer of 2-butene, where the two largest substituents are positioned on opposite sides of the double bond.