Organic chemistry 101/11/16 期中考試 102/01/11 期末考試 講義位址 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 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 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 1s  2s  2p  3s  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

Gilbert N. Lewis Valence shellValence shell: the outermost electron shell of an atom Valence electronsValence electrons: electrons in the valence shell of an atom; these electrons are used in forming chemical bonds Lewis structure of an atomLewis 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 structures

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 bondIonic 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 bondCovalent 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: sp 3 Orbitals and the Structure of Methane  Carbon has four electrons in its valence shell (2s 2 2p 2 )  An s orbital and three p orbitals can combine, or hybridize, to form four equivalent atomic orbitals (sp 3 hybrids) with tetrahedral orientation

Why do you think a C-H bond (109 pm) is longer than an H-H bond (74 pm) Bond strength: 439 kJ/mol

Hybridization: sp 3 Orbitals and the Structure of Ethane Bond strength of C-H: 421 kJ/mol Bond strength of C-C: 377 kJ/mol

Hybridization: sp 2 Orbitals and the Structure of Ethylene  An s orbital combines with only two of three p orbitals to form three equivalent atomic orbitals (sp 2 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 Electronegativity: a measure of the force of an atom ’ s attraction for the electrons it shares in a chemical bond with another atom

Na + -Cl - Cl-Cl H-Cl

Acids and Bases: The Bronsted-Lowry Definition HA + H 2 O  A - + H 3 O + Ka = [A - ] + [H 3 O + ] [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