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Chemistry LibreTexts

2: Structure and Properties of Organic Molecules

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  • Learning Objectives

    After reading this chapter and completing ALL the exercises, a student can be able to

    • define the terms "sterics" and "electrostatics" - refer to section 2.1
    • write and interpret molecular orbital (MO) diagrams - refer to section 2.2
    • predict the hybridization and geometry of atoms in a molecule - refer to section 2.3
    • draw accurate 3-D representations of molecules with approximate bond angles - refer to section 2.3
    • recognize conjugated pi bond systems - refer to section 2.4
    • recognize that benzene is aromatic - refer to section 2.4
    • identify the orbitals occupied by lone pair electrons - refer to section 2.5
    • distinguish between bonds that can rotate and those that cannot - refer to section 2.6
    • recognize the relationships between constitutional (structural) isomers, conformational isomers, and geometric isomers - refer to section 2.7
    • apply the homologous series to organic molecules with 1-10 carbons - refer to section 2.8
    • classify hydrocarbons as saturated or unsaturated - refer to section 2.8
    • classify hydrocarbons as alkanes, alkenes, alkynes, cycloalkanes, or aromatics (arenes) - refer to section 2.8
    • recognize and classify the common functional groups of organic chemistry (alkanes, alkenes, alkynes, alkyl halides, alcohols, amines, ethers, aldehydes, ketones, carboxylic acids, esters, and amides - refer to section 2.9
    • determine the dominant intermolecular forces (IMFs) of organic compounds - refer to section 2.10
    • predict the relative boil points of organic compounds - refer to section 2.11
    • predict whether a mixture of compounds will a form homogeneous or heterogeneous solution - refer to section 2.12
    • distinguish between organic compounds that are H-bond donors versus H-bond acceptors - refer to section 2.13
    • apply the terms sterics and electrostatics to organic compounds - refer to sections 2.1- 2.13

    • 2.1: Pearls of Wisdom
      A few "pearls of wisdom" about "sterics" and "electrostatics" to provide context when applying the concepts of general chemistry to  organic compounds.
    • 2.2: Molecular Orbital (MO) Theory (Review)
      Molecular orbital (MO) theory describes the behavior of electrons in a molecule in terms of combinations of the atomic wavefunctions.
    • 2.3: Hybridization and Molecular Shapes (Review)
      Hybridization and the Valence Shell Electron Pair Repulsion Theory effectively predict the three-dimensional structure of organic molecules.  Since carbon can only form four bonds, we can limit our study to the tetrahedral, trigonal planar, and linear electron geometries.
    • 2.4 Conjugated Pi Bond Systems
      A conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability.  Recognizing the conjugated systems is helpful in determining reaction pathways.
    • 2.5: Lone Pair Electrons and Bonding Theories
      The chemical reactivity of lone pair electrons can be determined from the identity of the orbital they occupy.  This concept will be further refined when we study aromaticity.
    • 2.6: Bond Rotation
      Single bonds can rotate, while double and triple bonds are rigid.
    • 2.7: Isomerism Introduction
      Structural (constitutional) isomers have the same molecular formula but a different bonding arrangement among the atoms. Stereoisomers have identical molecular formulas and arrangements of atoms. They differ from each other only in the spatial orientation of groups in the molecule.
    • 2.8: Hydrocarbons & the Homologous Series
      Since we will be spending the rest of the course working with compounds with a carbon backbone, there is no time like the present to learn the homologous series, the names for simple, straight hydrocarbon chains and branches.
    • 2.9: Organic Functional Groups
      Functional groups are to organic chemistry what ions are to general chemistry.  We simply must be able to recognize and distinguish between functional grouops to learn organic chemistry.
    • 2.10: Intermolecular Forces (IMFs) - Review
      Intermolecular forces (IMFs) have many useful applications in organic chemistry. For students interested in biochemistry, the concepts of IMFs are called non-covalent interactions when they occur within a large biological molecule creating secondary and tertiary structure.
    • 2.11: Intermolecular Forces & Relative Boiling Points (bp)
      The relative strength of the intermolecular forces (IMFs) can be used to predict the relative boiling points of pure substances.
    • 2.12: Intermolecular Forces & Solubilities
      Organic chemistry can perform reactions in non-aqueous solutions using organic solvents.  It is important to start considering the solvent as a reaction parameter and the solubility of each reagent.
    • 2.12: Additional Practice Problems
    • 2.13: Organic Functional Groups: H-bond donors & H-bond acceptors
      When evaluating organic compounds, we want to visualize the compounds in their three-dimensional shapes exerting intermolecular forces on their environment.  Because reactions will occur in aqueous and non-aqueous (organic) solutions, it is important to recognize which functional groups are both H-bond donors and H-bond acceptors and which groups are only H-bond acceptors.
    • 2.14: Additional Exercises
      This section has additional exercises for the key learning objectives of this chapter.
    • 2.15 Solutions to Additional Exercises
      This section has the solutions to the exercises in the previous section.