Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Bond valence method wikipedia , lookup
History of molecular theory wikipedia , lookup
Atomic theory wikipedia , lookup
Atomic orbital wikipedia , lookup
Molecular orbital wikipedia , lookup
Resonance (chemistry) wikipedia , lookup
Metallic bonding wikipedia , lookup
Hypervalent molecule wikipedia , lookup
Bent's rule wikipedia , lookup
Electron configuration wikipedia , lookup
Organic Chemistry 6th Edition Paula Yurkanis Bruice Chapter 1 Electronic Structure and Bonding Acids and Bases © 2011 Pearson Education, Inc. 1 Organic Chemistry • Carbon-containing compounds were once considered “organ compounds” available only from living organisms. • The synthesis of the simple organic compound urea in 1828 showed that organic compounds can be prepared in the laboratory from non-living material. • Today, organic natural products are routinely synthesized in the laboratory. © 2011 Pearson Education, Inc. 2 Why Carbon? • Carbon neither gives up nor accepts electrons because it is in the center of the second periodic row. • Consequently, carbon forms bonds with other carbons and other atoms by sharing electrons. • The capacity of carbon to form bonds in this fashion makes it the building block of all living organisms. © 2011 Pearson Education, Inc. 3 Why Study Organic Chemistry? • Since carbon is the building block of all living organisms, a knowledge of Organic Chemistry is a prerequisite to understanding Biochemistry, Medicinal Chemistry, Chemical Engineering, Polymer, and Pharmacology. • Indeed, Organic Chemistry is a required course for studying Chemical Engineering, Pharmacy, Medicine, and Dentistry. • Admission into these professional programs is highly dependent on your performance in Organic Chemistry. © 2011 Pearson Education, Inc. 4 Examples of Organic Compounds Used as Drugs Methotrexate, Anticancer Drug 5-Fluorouracil, Colon Cancer Drug Tamiflu, Influenza Drug AZT, HIV Drug 5 © 2011 Pearson Education, Inc. Examples of Organic Compounds Used as Drugs Haldol, Antipsychotic Elavil, Antidepressant Prozac, Antidepressant Viagra, Treats Erectile Dysfunction 6 © 2011 Pearson Education, Inc. 1.1 The Structure of an Atom • An atom consists of electrons, positively charged protons, and neutral neutrons. • Electrons form chemical bonds. • Atomic number: numbers of protons in its nucleus • Mass number: the sum of the protons and neutrons of an atom • Isotopes have the same atomic number but different mass numbers. • The atomic weight: the average weighted mass of its atoms • Molecular weight: the sum of the atomic weights of all the atoms in the molecule © 2011 Pearson Education, Inc. 7 1.2 The Distribution of Electrons in an Atom • Quantum mechanics uses the mathematical equation of wave motions to characterize the motion of an electron around a nucleus. • Wave functions or orbitals tell us the energy of the electron and the volume of space around the nucleus where an electron is most likely to be found. • The atomic orbital closer to the nucleus has the lowest energy. • Degenerate orbitals have the same energy. © 2011 Pearson Education, Inc. 8 The ground-state electronic configuration describes the orbitals occupied by the atom’s electrons with the lowest energy © 2011 Pearson Education, Inc. 9 The following principles determine which orbitals electrons occupy: • The Aufbau principle: an electron always goes to the available orbital with the lowest energy • The Pauli exclusion principle: only two electrons can occupy one atomic orbital and the two electrons have opposite spin • Hund’s rule: electrons will occupy empty degenerated orbitals before pairing up in the same orbital © 2011 Pearson Education, Inc. 1 1.3 IONIC AND COVALENT BONDS Lewis’s theory: an atom will give up, accept, or share electrons in order to achieve a filled outer shell or an outer shell that contains eight electrons → octet rule © 2011 Pearson Education, Inc. 11 Ionic Bonds : Formed by the Transfer of Electrons Attractive forces between opposite charges are called electrostatic attractions © 2011 Pearson Education, Inc. 12 Covalent Bonds : Formed by Sharing Electrons © 2011 Pearson Education, Inc. 13 • Equal sharing of electrons: nonpolar covalent bond (e.g., H2) • Sharing of electrons between atoms of different electronegativities: polar covalent bond (e.g., HF) © 2011 Pearson Education, Inc. 14 Polar covalent bonds © 2011 Pearson Education, Inc. 15 A Polar Bond Has a Dipole Moment • A polar bond has a negative end and a positive end dipole moment (D) = m = e x d (e) : magnitude of the charge on the atom (d) : distance between the two charges © 2011 Pearson Education, Inc. 16 Electrostatic Potential Maps © 2011 Pearson Education, Inc. 17 1.4 HOW THE STRUCTURE OF A COMPOUND IS REPRESENTED: Lewis Structure Formal charge = number of valence electrons – (number of lone pair electrons +1/2 number of bonding electrons) © 2011 Pearson Education, Inc. 18 Nitrogen has five valence electrons Carbon has four valence electrons Hydrogen has one valence electron and halogen has seven © 2011 Pearson Education, Inc. 19 Important Bond Numbers Neutral Cationic Anionic © 2011 Pearson Education, Inc. 20 Non-Octet Species • In the 3rd and 4th rows, expansion beyond the octet to 10 and 12 electrons is possible. Sulfuric Acid Periodic Acid Phosphoric Acid • Reactive species without an octet such as radicals, carbocations, carbenes, and electropositive atoms (boron, beryllium). Nitric Oxide Radical Radical, Mammalian Signaling Agent Carbocation © 2011 Pearson Education, Inc. Carbene Borane 21 Kekulé Structures Condensed Structures 22 © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. 23 1.5 ATOMIC ORBITALS An orbital tells us the volume of space around the nucleus where an electron is most likely to be found The s Orbitals © 2011 Pearson Education, Inc. 24 The p Orbitals © 2011 Pearson Education, Inc. 25 1.6 Molecular Orbitals • Molecular orbitals belong to the whole molecule. • s bond: formed by overlapping of two s orbitals. • Bond strength/bond dissociation: energy required to break a bond or energy released to form a bond. © 2011 Pearson Education, Inc. 26 The change in energy that occurs as two 1s atomic orbitals approach each other. The internuclear distance at minimum energy is the length of the H-H covalent bond. © 2011 Pearson Education, Inc. 27 In-phase overlap : bonding MO out-of-phase overlap : antibonding MO © 2011 Pearson Education, Inc. 28 Sigma bond (s) is formed by end-on overlap of two p orbitals: A s bond is stronger than a p bond © 2011 Pearson Education, Inc. 29 Pi bond (p) is formed by sideways overlap of two parallel p orbitals: © 2011 Pearson Education, Inc. 30 1.7 HOW SINGLE BONDS ARE FORMED IN ORGANIC COMPOUNDS Bonding in Methane © 2011 Pearson Education, Inc. 31 Hybridization of One s and Three p Orbitals © 2011 Pearson Education, Inc. 32 The orbitals used in bond formation determine the bond angles • Tetrahedral bond angle: 109.5° • Electron pairs spread themselves into space as far from each other as possible © 2011 Pearson Education, Inc. 33 The Bonds in Ethane © 2011 Pearson Education, Inc. 34 Hybrid Orbitals of Ethane © 2011 Pearson Education, Inc. 35 1.8 Bonding in Ethene: A Double Bond © 2011 Pearson Education, Inc. 36 © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. 1.9 Bonding in Ethyne: A Triple Bond © 2011 Pearson Education, Inc. 38 © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. 1.10 THE BONDS IN THE METHYL CATION, THE METHYL RADICAL, AND THE METHYL ANION Bonding in the Methyl Cation © 2011 Pearson Education, Inc. 40 Bonding in the Methyl Radical Bonding in the Methyl Anion © 2011 Pearson Education, Inc. 41 1.11 THE BONDS IN WATER © 2011 Pearson Education, Inc. 42 1.12 THE BONDS IN AMMONIA AND IN THE AMMONIUM ION © 2011 Pearson Education, Inc. 43 © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. 1.13 THE BOND IN A HYDROGEN HALIDE © 2011 Pearson Education, Inc. 45 Summary • The shorter the bond, the stronger it is • The greater the electron density in the region of orbital overlap, the stronger is the bond • The more s character, the shorter and stronger is the bond • The more s character, the larger is the bond angle © 2011 Pearson Education, Inc. 46 1.15 THE DIPOLE MOMENTS OF MOLECULES The vector sum of the magnitude and the direction of the individual bond dipole determines the overall dipole moment of a molecule © 2011 Pearson Education, Inc. 47 1.16 AN INTRODUCTION TO ACIDS AND BASES Brø nsted–Lowry Acids and Bases; Acid: donates a proton Base: accepts a proton © 2011 Pearson Education, Inc. 48 1.17 pKa AND pH © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. 1.18 ORGANIC ACIDS AND BASES Protonated alcohols and protonated carboxylic acids are very strong © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. acids An amine can behave as an acid or as a base © 2011 Pearson Education, Inc. 52 © 2011 Pearson Education, Inc. 53 1.19 HOW TO PREDICT THE OUTCOME OF AN ACID—BASE REACTION © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. 1.20 HOW TO DETERMINE THE POSITION OF EQUILIBRIUM • Strong reacts to give weak • The weaker the base, the stronger is its conjugate acid • Stable bases are weak bases © 2011 Pearson Education, Inc. 55 1.21 HOW THE STRUCTURE OF AN ACID AFFECTS ITS pKa VALUE Electronegativity © 2011 Pearson Education, Inc. 56 Hybridization © 2011 Pearson Education, Inc. 57 Size The stronger acid will have its proton attached to the largest atom size overrides electronegativity © 2011 Pearson Education, Inc. 58 © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. 1.22 HOW SUBSTITUENTS AFFECT THE STRENGTH OF AN ACID Inductive electron withdrawal increases the acidity of a conjugate acid © 2011 Pearson Education, Inc. 60 1.23 AN INTRODUCTION TO DELOCALIZED ELECTRONS Acetic acid is more acidic than ethanol The delocalized electrons in acetic acid are shared by more than two atoms, thereby stabilizing the conjugated base © 2011 Pearson Education, Inc. 61 1.24 A SUMMARY OF THE FACTORS THAT DETERMINE ACID STRENGTH 1. Size: As the atom attached to the hydrogen increases in size, the strength of the acid increases 2. Electronegativity 3. Hybridization © 2011 Pearson Education, Inc. 62 4. Inductive effect 5. Electron delocalization © 2011 Pearson Education, Inc. 63 1.27 LEWIS ACIDS AND BASES • Lewis acid: non-proton-donating acid; will accept two electrons • Lewis base: electron pair donors © 2011 Pearson Education, Inc. 64