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Book

Cover Organic Chemistry

Tadashi Okuyama and Howard Maskill

Organic Chemistry begins by looking at chemical bonding and molecules. The text moves on to molecular structure and the shape of organic molecules. Other topics covered include organic compounds, conjugation, pi-electron delocalization, aromaticity, acids and bases. Chapters also examine organic reactions, nucleophilic addition, stereochemistry, reactions of alcohols and addition reactions of alkenes and alkynes. There are also chapters on enolate anions, enolate ions, and reactions of nucleophiles with alkenes and aromatic compounds. The text next turns to polycyclic and heterocyclic aromatic compounds, rearrangement reactions, pericyclic reactions, and rearrangement reactions involving polar molecules and ions. Finally, the text discusses biomolecules, chemistry of biomolecules, and the structural determination of organic compounds.

Chapter

Cover Organic Chemistry

Conjugation, π-Electron Delocalization, and Aromaticity  

This chapter begins with a discussion on extended π bonds and the concept of conjugation. It stresses that the C=C double bond is made up of a σ bond and a π bond, and the characteristic chemical properties of ethene come mainly from the π bond. The chapter also highlights that two C=C double bonds separated by a single σ bond are also able to interact by sideways overlap of their π molecular orbitals or MOs (called a conjugative interaction) in a conjugated system. The chapter then introduces stabilization or delocalization energy. It investigates how constituent π and p orbitals of appropriate energy and symmetry within a molecule (or ion) interact to give the new MOs of a conjugated system, and how the conjugation can be described by resonance. Next, the chapter considers the electronic structure of benzene and the nature of aromaticity.

Chapter

Cover Making the Transition to University Chemistry

Bonding and Molecular Shape  

This chapter discusses bonding and molecular shape of electrons. A covalent bond occurs when atoms share a pair of similar electrons. Modern theories on covalent bonding are dominated by molecular orbital theory. Polar covalent bonds occur when different atoms share the electron pair unequally due to electronegativity. With benzene being the most familiar molecule of the bonding, delocalization happens when more than two atoms are involved in the bonding. The valence-shell electron-pair repulsion (VSEPR) theory can help us to visualize the shapes of simple molecules. Additionally, ionic bonding occurs when an atom transfers an electron to another atom and the ions formed a crystal lattice electrostatically.

Chapter

Cover Chemical Structure and Reactivity

Electrons in molecules: polyatomics  

This chapter begins by showing how symmetry considerations make it possible to construct molecular orbital diagrams for simple triatomics. In these molecules, the MOs extend over all the atoms—that is, the bonding is delocalized. In fact, it is a general feature of the MO approach that atomic orbitals on many atoms contribute to each MO. Unfortunately, this means that as the number of atoms (and hence orbitals) increases, it rapidly becomes almost impossible to draw up useful qualitative MO diagrams. Hybrid atomic orbitals provide a convenient localized description of bonding in larger molecules. Due to the directional nature of the hybrid atomic orbitals, their overlap gives bonds which are localized between two atoms. This greatly simplifies the description of the bonding in larger molecules, as it can be broken down into a set of interactions between just two atoms at a time.

Chapter

Cover Organic Chemistry

Delocalization and conjugation  

This chapter focuses on delocalization and conjugation. Colours result from the interaction of light with the pigments in different things—some frequencies of light are absorbed, others scattered. Inside our eyes, chemical reactions detect these different frequencies and convert them into electrical nerve impulses sent to the brain. All these pigments have one thing in common—lots of double bonds. The chapter looks at the properties, including colour, of molecules that have several double bonds. These properties depend on the way the double bonds join up, or conjugate, and the resulting delocalization of the electrons within them. The chapter then considers the structure of ethane, the UV–visible spectrum, the allyl system, and aromaticity.

Chapter

Cover Chemical Structure and Reactivity

Bonding in solids  

This chapter focuses on bonding in solids, particularly metallic bonding. In solids, the overlap between orbitals on different atoms can give rise to crystal orbitals which extend throughout the material; these orbitals are analogous to delocalized molecular orbitals. The crystal orbitals which arise from a particular set of atomic orbitals form a band, which can hold a certain number of electrons. The electrical conductivity of metals is the result of partially filled bands; insulators have full bands, but in semiconductors there is a small gap between a filled and an empty band. The lattice enthalpy of an ionic solid can be estimated using a simple electrostatic model. It depends on the size (radii) of the ions and their three-dimensional arrangement in the crystal.

Chapter

Cover Chemistry for the Biosciences

Compounds and chemical bonding: bringing atoms together  

This chapter examines compounds and chemical bonding. A compound is a substance that comprises atoms of more than one element. Chemical bonds hold the components of a compound together and are formed by the redistribution of valence electrons between atoms. According to the octet rule, valence electrons are redistributed so that atoms achieve full valence shells that typically contain eight electrons. The chapter then differentiates between the two types of chemical bond: ionic and covalent. An ionic bond forms when one or more electrons are totally transferred from one atom to another to generate an ionic compound. A covalent bond, however, forms when one or more pairs of electrons are shared between atoms to generate a covalent compound. The chapter looks at polarized bonds, in which electrons are shared unequally between two nuclei, and discusses how valency describes the number of chemical bonds an atom of a given element can participate in. It also describes chemical bonding in terms of atomic and molecular orbitals before discussing aromatic compounds and polyatomic ionic compounds.

Chapter

Cover Stereoelectronic Effects

Substitutions at saturated centres  

This chapter focuses on substitutions at saturated centres. Substitution, or displacement, reactions are the commonest of all organic reactions, and substitutions at sp3-carbon were the first to be studied in depth. We know that two, conceptually quite different, mechanisms may be involved. The reaction can be concerted, with the new bond forming as the old bond breaks, or stepwise, with separate bond-breaking and bond-making steps. It can be a cation, as in the SN1 mechanism for nucleophilic substitution; an anion, in which case the reaction is electrophilic substitution; or a radical. The chapter then looks at concerted nucleophilic substitution; stereoelectronic barriers to intramolecular alkyl-group transfer; and the stabilization of the SN2 transition state by delocalization.