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Organic Chemistry
Table of Contents
Unit 3 Overview: Alkanes: Structure and Stereochemistry
3.1 Functional Groups
3.2 Alkanes and Alkane Isomers
3.3 Alkyl Groups
3.4 Naming Alkanes
3.5 Properties of Alkanes
3.6 Conformations of Ethane
3.7 Conformations of Other Alkanes

Alkane nomenclature is all about naming carbon-based molecules systematically. It involves identifying the longest carbon chain, naming substituents, and following specific rules for numbering and ordering.

Understanding these rules is crucial for communicating molecular structures accurately. Mastering alkane nomenclature sets the foundation for naming more complex organic compounds and understanding their properties and reactions.

Alkane Nomenclature

Longest carbon chain identification

  • Find the longest continuous chain of carbon atoms in the molecule this chain determines the parent name of the alkane
  • Count the number of carbon atoms in the longest chain to determine the base name
    • Names based on number of carbons: Methane (1), Ethane (2), Propane (3), Butane (4), Pentane (5), Hexane (6), Heptane (7), Octane (8), Nonane (9), Decane (10)
    • For chains longer than 10 carbons, use Greek prefixes: undec- (11), dodec- (12), tridec- (13), tetradec- (14), pentadec- (15), and so on (hexadec-, heptadec-, octadec-, nonadec-, eicos-)
  • If the carbon chain is unbranched, the IUPAC name is simply the name of the parent chain no additional nomenclature needed (hexane)

Alkyl substituent naming

  • Identify alkyl substituents (branches) attached to the main carbon chain
    • Alkyl groups named based on number of carbons: Methyl (1 carbon), Ethyl (2 carbons), Propyl (3 carbons), Butyl (4 carbons), Pentyl (5 carbons)
  • Number the parent chain starting from the end closest to the first substituent gives the substituents the lowest possible locant numbers
  • Determine the position of each substituent by the number of the carbon it is attached to on the parent chain this number is the locant
  • If there are multiple substituents, list them in alphabetical order when naming
    • Ignore prefixes like "di-", "tri-", etc. when alphabetizing (ethyl before dimethyl)
  • Use Greek prefixes to indicate the number of identical substituents
    • Prefixes: di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6), and so on (hepta-, octa-, nona-, deca-)
  • Separate locant numbers with commas and place a dash between the last number and the parent chain name (2,3-dimethylbutane)

Skeletal structure drawing

  • Identify the parent chain based on the IUPAC name
    • Parent chain name indicates the number of carbons (heptane = 7 carbon chain)
  • Draw the parent chain as a straight line of carbon atoms, each carbon represented by the end of a line segment or a vertex
    • Do not explicitly draw the carbon (C) or hydrogen (H) atoms they are implied
  • Attach the substituents to the parent chain at the appropriate positions indicated by the locant numbers
    • Draw substituents as lines branching off from the parent chain at the specified carbons
  • Ensure each carbon atom has four total bonds (including implicit C-H bonds not shown) satisfies the tetravalency of carbon
    • Example: For 3-ethylpentane, draw a 5-carbon chain with an ethyl group attached to the 3rd carbon

Structural Representations and Isomers

  • Structural formula: A detailed representation showing all atoms and bonds in a molecule
  • Condensed structural formula: A simplified representation that shows carbon-carbon bonds but implies hydrogen atoms
  • Constitutional isomers: Compounds with the same molecular formula but different structural arrangements of atoms
  • Hydrocarbons: Organic compounds composed only of carbon and hydrogen atoms, with alkanes being a specific class of saturated hydrocarbons

Key Terms to Review (43)

Methylene group: A methylene group is a functional group consisting of two hydrogen atoms bound to a carbon atom, which is then connected to other parts of a molecule. In the context of alkenes, it often refers to the CH2 unit that can be part of the alkene's structure.
Secondary metabolite: Secondary metabolites are organic compounds produced by plants, fungi, or bacteria that are not directly involved in the normal growth, development, or reproduction of the organism. Unlike primary metabolites, which are essential for life, secondary metabolites often play a role in plant defense mechanisms and interactions with other organisms.
Optical isomers: Optical isomers are molecules that have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientation of their atoms in space, leading to different optical activities. These isomers are non-superimposable mirror images of each other, much like left and right hands.
Urethane: Urethane, also known as ethyl carbamate, is a compound formed from the reaction between an alcohol and an isocyanate group as part of the step-growth polymerization process. It is a key building block in the production of polyurethanes, which are versatile synthetic polymers used in a wide range of applications from foams to elastomers.
IUPAC system of nomenclature: The IUPAC system of nomenclature is a standardized method for naming organic compounds devised by the International Union of Pure and Applied Chemistry. It ensures clarity and uniformity in the naming process, allowing chemists worldwide to understand precisely which compound is being referred to.
Constitutional isomers: Constitutional isomers are compounds that have the same molecular formula but differ in the sequence in which their atoms are connected. These variations lead to molecules with distinct physical and chemical properties, despite having the same numbers of each type of atom.
Primary (RNH2): In organic chemistry, a primary amine is an amine where the nitrogen atom is attached to one alkyl or aryl group and two hydrogen atoms. It can be represented as RNH2, where R represents an alkyl or aryl group.
Hydrocarbon: Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon atoms. They form the framework for alkanes and vary in size, structure, and properties based on the arrangement of their atoms.
Ethane: Ethane is the simplest alkane, a saturated hydrocarbon with the chemical formula C2H6. It is a key term in understanding the concepts of sp3 hybrid orbitals, the structure of alkanes, and their properties.
Methane: Methane is the simplest and most abundant alkane, with a chemical formula of CH4. It is a colorless, odorless, and flammable gas that serves as the primary component of natural gas and plays a crucial role in organic chemistry and the study of alkanes.
Condensed Structural Formula: A condensed structural formula is a simplified way of representing the structure of a chemical compound. It focuses on the connectivity of atoms, omitting certain details to provide a concise and easy-to-read representation of the molecule.
Isomers: Isomers are molecules that have the same molecular formula but different structural arrangements of atoms. These structural differences lead to distinct physical and chemical properties, making isomers an important concept in organic chemistry.
Propane: Propane is a simple alkane hydrocarbon with the chemical formula C3H8. It is a colorless, odorless, and flammable gas that is widely used as a fuel source for heating, cooking, and transportation. Propane's properties and behavior are important in understanding the topics of alkanes, alkane isomers, and the interpretation of 1H NMR spectra.
Quaternary: Quaternary refers to a carbon atom that is bonded to four other carbon atoms, resulting in a highly substituted carbon center. This structural feature is an important consideration in the context of alkyl groups and the systematic naming of alkanes.
Pentyl: Pentyl is a five-carbon alkyl group, derived from the alkane pentane, that is commonly used in organic chemistry to represent a specific structural feature or functional group. This term is particularly relevant in the context of understanding alkyl groups and the systematic naming of alkanes.
Propyl: Propyl is a three-carbon alkyl group with the chemical formula -CH2CH2CH3. It is an important functional group in organic chemistry, particularly in the context of alkanes, alkyl groups, and the naming of organic compounds.
Nomenclature: Nomenclature refers to the systematic naming and classification of chemical compounds based on established rules and conventions. It is a crucial aspect of organic chemistry, as it provides a standardized way to identify and communicate the structures of various compounds.
Heptane: Heptane is a straight-chain alkane hydrocarbon with the molecular formula C7H16. It is a colorless, flammable liquid that is commonly used as a solvent and as a component in gasoline and other fuels.
Secondary: Secondary, in the context of organic chemistry, refers to a specific type of carbon atom arrangement within alkyl groups and the naming of alkanes. It describes a carbon atom that is bonded to two other carbon atoms, resulting in a distinct structural and reactivity profile.
Parent Chain: The parent chain is the longest continuous carbon chain in a molecule, which serves as the basis for naming organic compounds. This key term is central to the systematic nomenclature used across various classes of organic compounds, including alkanes, alkenes, aromatic compounds, alcohols, phenols, and carboxylic acid derivatives.
Alkanes: Alkanes are a class of saturated hydrocarbons composed entirely of single-bonded carbon and hydrogen atoms. They are the simplest organic compounds and serve as the foundation for many other organic molecules and reactions.
Ethyl: Ethyl is a two-carbon alkyl group with the chemical formula -CH2CH3. It is a common substituent group in organic chemistry and plays a crucial role in understanding various topics, including alkanes, alkyl groups, naming conventions, and carbocation rearrangements.
Butane: Butane is a simple alkane hydrocarbon with the chemical formula C4H10. It is a colorless, odorless gas that is commonly used as a fuel source and in the production of other chemicals. Butane is an important compound in the context of organic chemistry, particularly in the study of alkanes and alkane isomers, as well as the application of 13C NMR spectroscopy.
Pentane: Pentane is a straight-chain alkane with the molecular formula C$_{5}$H$_{12}$. It is a colorless, volatile, and flammable hydrocarbon that is widely used in various industrial and commercial applications.
Constitutional Isomers: Constitutional isomers are a type of structural isomerism where molecules have the same molecular formula but differ in the connectivity or arrangement of their atoms. This concept is essential in understanding the properties and behavior of organic compounds across various topics in chemistry.
IUPAC: IUPAC, or the International Union of Pure and Applied Chemistry, is the authoritative body responsible for establishing standardized rules and guidelines for the naming and representation of chemical compounds. This term is crucial in the context of organic chemistry, as it provides a systematic and unambiguous way to name and identify various classes of organic molecules.
Alkyl Groups: Alkyl groups are hydrocarbon substituents derived from alkanes by the removal of one hydrogen atom. They are non-polar, saturated, and can be straight-chain or branched. Alkyl groups play a crucial role in understanding the properties and behavior of various organic compounds, including alkanes, alkenes, and benzene derivatives.
Hexane: Hexane is a straight-chain alkane with the molecular formula C6H14. It is a colorless, volatile, and flammable liquid that is widely used as a solvent and in the production of various chemicals and fuels.
Primary: The term 'primary' refers to something that is first, original, or fundamental in a hierarchy or sequence. In the context of organic chemistry, the term 'primary' is used to describe specific structural features of alkyl groups and alkanes.
Butyl: Butyl is a four-carbon alkyl group, derived from the alkane butane, that is commonly used in organic chemistry. It is represented by the formula -CH2CH2CH2CH3 and is an important structural component in many organic compounds.
Substituents: Substituents are atoms or functional groups that replace hydrogen atoms in a molecule's structure. They are an essential concept in organic chemistry, as they play a crucial role in determining the properties, reactivity, and naming of various organic compounds.
Methyl: The methyl group is a simple alkyl group consisting of a single carbon atom bonded to three hydrogen atoms. It is denoted by the formula -CH3 and is the most basic and common alkyl group found in organic chemistry. The methyl group plays a crucial role in various organic reactions and structural features across several key topics in this course.
Tertiary: Tertiary refers to a specific type of carbon atom arrangement within organic compounds, particularly in the context of alkyl groups and the naming of alkanes. It describes a carbon atom that is bonded to three other carbon atoms.
Hydrocarbon: A hydrocarbon is a chemical compound consisting entirely of hydrogen and carbon atoms. These molecules form the basis for organic chemistry and are the simplest organic compounds, serving as the building blocks for more complex organic molecules.
Branching: Branching refers to the presence of alkyl substituents attached to the main carbon chain of an alkane molecule. This structural feature has a significant impact on the physical and chemical properties of the compound, as well as its naming and classification.
Numbering System: The numbering system is a fundamental concept in organic chemistry that provides a standardized way to identify and name the carbon atoms within a molecule. It is particularly crucial in the context of naming alkanes, as it allows for the unambiguous identification of the position and arrangement of substituents.
Octane: Octane is a measure of the anti-knock properties of a fuel used in internal combustion engines, particularly in gasoline engines. It is a crucial parameter in determining the suitability and performance of a fuel for a specific engine design.
Nonane: Nonane is a straight-chain alkane with the molecular formula C9H20. It is a colorless, odorless, and flammable liquid hydrocarbon that is commonly used as a solvent and in the production of other chemicals.
Decane: Decane is a straight-chain alkane with the molecular formula C10H22. It is a colorless, odorless, and flammable liquid that is an important component in various petroleum-based products and industrial applications.
Skeletal Structure: Skeletal structure refers to the arrangement and organization of the atoms or molecules that make up the framework of organic compounds, particularly in the context of alkanes. It provides a visual representation of the connectivity and spatial orientation of the carbon atoms and their attached hydrogen atoms.
Longest Carbon Chain: The longest carbon chain refers to the main carbon skeleton in an organic molecule, which determines the basic structure and nomenclature of the compound. This term is particularly important in the context of naming alkanes, as the length of the longest carbon chain is a key factor in determining the root name of the molecule.
Locant: In organic chemistry, a locant is a number or symbol used to indicate the position of a substituent or functional group on a parent hydrocarbon chain or ring. Locants are essential for unambiguously naming and identifying the structure of organic compounds.
Structural Formula: The structural formula, also known as the line-angle formula or skeletal formula, is a graphical representation of the arrangement of atoms and bonds within a molecule. It provides a clear and concise way to depict the connectivity and spatial arrangement of the atoms, allowing for the identification and understanding of the chemical structure of a compound.