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Organic chemistry • 101/11/16 • 102/01/11 期中考試 期末考試 講義位址 http://www.aqua.ntou.edu.tw/chlin/ http://moodle.ntou.edu.tw/ Fundamentals of Organic Chemistry 7th Edition McMurry Thomson Brooks/Cole Organic chemistry • What is organic chemistry • Why should we study it Organic chemistry Organic chemistry: The study of the compounds of carbon (C) Over 30 million organic compounds have been identified ─about 1000 new ones are discovered or synthesized and identified each day! C is a small atom ─ It can share 4 valence electrons and form 4 covalent bonds ─ it can bond to one another and form long chains and rings ─ it is able to form an immense diversity of compounds, from methane to DNA Chapter 1 Structure and Bonding; Acids and Bases Atomic structure • Small dense nucleus, diameter 10-14 - 10-15 m, which made of neutrons and positively-charged protons. • Most of the mass of the atom is contained in its nucleus. • Extranuclear space, diameter 2 x 10-10 m (0.2 nm, 200 pm, 2Å), which contains negatively-charged electrons Electrons do not freely move in the space around a nucleus and are confined to regions of space called principle energy levels Orbitals • A region of space around a nucleus where electrons are found • A region of space where an electron or pair of electrons spends 90-95% of its time • 4 different kinds of orbitals, denoted s, p, d, f........ • All s orbitals have the shape of a sphere • A p orbital consists of two lobes separated by a node • Different layers, or electron shells, contain different numbers and kinds of orbitals • Each orbital can be occupied by 2 electrons • Electrons in lower numbered shells are nearest to the positively charged nucleus and are held most strongly by it; these electrons are said to be lowest in energy Electron Configuration of Atoms The lowest-energy arrangement, or ground-state electron configuration, of an atom is a description of the orbitals that the atom’s electrons occupy • Rule 1: The orbitals of lowest energy are filled first, according to the order 1s2s2p3s 3p 4s 3d 4p 5s 4d 5p • Rule 2: Only two electrons can occupy an orbital, and they must be of opposite spin • Rule 3: If two or more empty orbitals of equal energy are available, one electron occupies each with the spins parallel until all orbitals are half-full Ground-State electron configuration Lewis structures • Gilbert N. Lewis • Valence shell: the outermost electron shell of an atom • Valence electrons: electrons in the valence shell of an atom; these electrons are used in forming chemical bonds • Lewis structure of an atom – the symbol of an element surrounded by a number of bots equal to the number of electrons in the valence shell of the atom Lewis Structure: The symbol of an element surrounded by a number of dots equal to the number of electrons in the valence (outmost) shell of the atom The Nature of Chemical Bonds • Atoms bond together so that each atom in the bond acquires the electron configuration of the noble-gas closest it in atomic number – Octet rule: The tendency to react in ways that achieve an outer shell of eight valence electrons • Ionic bond: a chemical bond resulting from the electrostatic attraction of an anion and a cation (Na+ Cl-) – an atom that gains electrons becomes an anion – an atom that loses electrons becomes a cation • Covalent bond: a chemical bond resulting from two atoms sharing one or more pairs of electrons Forming Covalent Bonds: Valence Bond Theory A covalent bond forms when two atoms approach each other closely and a singly occupied orbital on one atom overlaps a singly occupied orbital on the other The electrons are now paired in the overlapping orbitals and are attracted to the nuclei of both atoms, thereby bonding the atoms together Bond strength: 436 kJ/mol Hybridization: sp3 Orbitals and the Structure of Methane Carbon has four electrons in its valence shell (2s2 2p2) An s orbital and three p orbitals can combine, or hybridize, to form four equivalent atomic orbitals (sp3 hybrids) with tetrahedral orientation Bond strength: 439 kJ/mol Why do you think a C-H bond (109 pm) is longer than an H-H bond (74 pm) Hybridization: sp3 Orbitals and the Structure of Ethane Bond strength of C-H: 421 kJ/mol Bond strength of C-C: 377 kJ/mol Hybridization: sp2 Orbitals and the Structure of Ethylene An s orbital combines with only two of three p orbitals to form three equivalent atomic orbitals (sp2 hybrids) One unhybridized 2p orbital remains unchanged Bond strength of C=C: 728 kJ/mol Hybridization: sp Orbitals and the Structure of Acetylene An s orbital combines with only one of three p orbitals to form three equivalent atomic orbitals (sp hybrids) Two unhybridized 2p orbital remains unchanged Acetylene (ethyne) Bond strength of C≡C: 965 kJ/mol Polar Covalent Bonds: Electronegativity • A molecule is polar if 1. It has polar bonds and 2. The center of partial positive charge lies at a different place within the molecule than the center of partial negative charge Electronegativity: a measure of the force of an atom’s attraction for the electrons it shares in a chemical bond with another atom Cl-Cl H-Cl Na+-Cl- Acids and Bases: The Bronsted-Lowry Definition HA + H2O A- + H3O+ -] + [H O+] [A 3 Ka = [HA] pKa = -logKa Organic Acids and Organic Bases Carboxylic acids Organic Acids and Organic Bases Carboxylic acids Acids and Bases: The Lewis Definition • A Lewis acid is a substance that has a vacant valence orbital and can thus accept an electron pair • A Lewis base is a substance that donates an electron pair • The donated pair of electrons is shared between Lewis acid and base in a newly formed covalent bond