Organic chemistry 100/11/11 期中考試 101/01/06 期末考試 講義位址 Essential Organic Chemistry 2nd Edition Paula Yurkanis Bruice Pearson Education, Inc.

What is organic chemistry – Organic: available only from living organisms? – Inorganic

Why study organic chemistry About all of the molecules that make life possible contain carbon Over 30 million organic compounds have been identified – about 1000 new ones are discovered or synthesized and identified each day!

Why carbon Small In the center of the 2 nd row of elements can share 4 valence electrons and form 4 covalent bonds is able to form an immense diversity of compounds, from methane to DNA

Chapter 1 Electronic Structure and covalent Bonding

THE STRUCTURE OF AN ATOM Small dense nucleus, diameter m, which made of neutrons and positively-charged protons. Extranuclear space, diameter 2 x m (0.2 nm, 200 pm, 2Å), which contains negatively- charged electrons. Most of the mass of the atom is contained in its nucleus. Electrons form chemical bonds An atom consists of electrons, positively charged protons, and neutral neutrons.

7 Atomic number: numbers of protons in its nucleus Mass number: the sum of the protons and neutrons of an atom – 12 C, 13 C, and 14 C (same atomic number, 6 protons) – Isotopes have the same atomic number but different mass numbers (neutrons). – 14 C is radioactive, decaying with a half-life of 5730 years 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

HOW THE ELECTRONS IN AN ATOM ARE DISTRIBUTED Electrons – Occupying a set of shells that surround the nucleus – The 1 st shell is the smallest and the one closest to the nucleus; the 2 nd shell is larger and extends farther from the nucleus – Each shell consists of subshells known as atomic orbitals designated by the letters s, p, d, f

Electrons – Each shell can contain up to n 2 atomic orbitals (n is the number of shell= 1,2,3, ) – Each shell contains one s orbital. – The atomic orbital closer to the nucleus has the lowest energy. ( 1s  2s  2p  3s  3p  4s  3d  4p  5s  4d  5p) – Each atomic orbital can contain no more than 2 electrons. The rules for determining the electronic configuration 1.An electron always goes to the available orbital with the lowest energy 2.Only two electrons can occupy one atomic orbital and the two electrons have opposite spin 3.Electrons will occupy empty degenerated orbitals before pairing up in the same orbital

Electrons in the inner shells are called core electrons. Electrons in the outermost shell are called valance electrons

IONIC AND COVALENT BONDS An atom is most stable if its outer shell is either filled or contains eight electrons and it has no electrons of higher energy – Octet rule: An atom will give up, accept, or share electrons in order to achieve a filled outer shell or an outer shell that contains 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

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

Attractive forces between opposite charges are called electrostatic attractions

Covalent bond: a chemical bond resulting from two atoms sharing one or more pairs of electrons

A hydrogen atom can achieve a completely empty shell by losing an electron and results in a positively charged hydrogen ion– proton A hydrogen atom can achieve a filled outer shell by gaining an electron, thereby forming in a negatively charged hydrogen ion– hydride ion

Polar Covalent Bonds: Electronegativity The atoms that share the bonding electrons in F-F or H-H covalent bond are identical—nonpolar covalent bond The covalent bond between atoms of different electronegativities—polar covalent bond

Na + -Cl - Cl-Cl H-Cl

Electrostatic Potential Maps

HOW THE STRUCTURE OF A COMPOUND IS REPRESENTED Lewis Structure Can show which atoms are bonded together Tell any atoms possess lone-pair electrons (nonbonding electrons) or have a formal charge

Kekulé structures Condensed structures

ATOMIC ORBITALS The s Orbitals An orbital tells us the volume of space around the nucleus where an electron is most likely to be found

The 2 nd shell contains three p orbitals A p orbital tells has two lobes The three 2p orbitals have the same energy The energy of 2p orbital is greater than that of a 2s orbital

HOW ATOMS FORM COVALENT BONDS 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 The covalent bond that is formed when the two orbitals overlap is called sigma (  ) bond

0.074 nm 1.Bond strength/bond dissociation: energy required to break a bond or energy released to form a bond. 2.Every covalent bond has a characteristic bond length and bond strength

HOW SINGLE BONDS ARE FORMED IN ORGANIC COMPOUNDS The Bonds in Methane

1.The four sp 3 orbitals adopt a spatial arrangement that keeps them as far from each other as possible 2.Methane forms covalent bonds using 4 equivalent sp 3 orbitals is called a tetrahedral carbon 3.Tetrahedral bond angle: °

The Bonds in Ethane

HOW A DOUBLE BOND IS FORMED: THE BONDS IN ETHENE

HOW A TRIPLE BOND IS FORMED: THE BONDS IN ETHYNE

BONDING IN THE METHYL CATION, THE METHYL RADICAL, AND THE METHYL ANION The methyl cation ( + CH 3 )

The methyl radical (·CH 3 ) The methyl anion ( - :CH 3 )

THE BONDS IN WATER

THE BONDS IN AMMONIA AND IN THE AMMONIUM ION

THE BOND IN A HYDROGEN HALIDE 2sp 3 3sp 3

SUMMARY: HYBRIDIZATION, BOND LENGTH, BOND STRENGTHS, AND BOND ANGLE All single bonds are  bonds All double bonds are composed of one  bond and one  bond All triple bonds are composed of one  bond and two  bonds

Chapter 2 Acids and Bases

Brønsted–Lowry defined an acid as a species that donates a proton, and a base as a species that accepts a proton AN INTRODUCTION TO ACIDS AND BASES When a compound loses a proton (HCl), the resulting species is called its conjugate base (Cl - ). When a compound accepts a proton (H 2 O), the resulting species is called its conjugate acid (H 3 O + ).

Water (H 2 O) can behave as either an acid or a base Acidity is a measure of the tendency of a compound to give up a proton Basicity is a measure of a compound’s affinity for a proton A strong acid has a strong tendency to give up a proton The weaker the base, the stronger is its conjugate acid The stronger the acid, the weaker is it conjugate base

pK a AND pH When a strong acid such as hydrogen chloride is dissolved in water, almost all the molecules dissociate. When a much weaker acid, such as acetic acid, is dissolved in water, very few molecules dissociate. K a = 10 7 K a = 1.74 x 10 -5

An Acid/Base Equilibrium Ka: The acid dissociation constant. The stronger the acid, the larger its Ka value and the smaller its pKa value. pK a = -log K a Very strong pK a < 1 moderately strong pK a = 1-3 Weak pK a = 3-5 Very weak pK a = 5-15 Extremely weak pK a > 15 K a = [H 3 O + ] [HA] [A - ]

pH is indicated the concentration of positively charge hydrogen ion [H + ] in the solution pH = -log [H + ] The lower the pH, the more acidic is the solution The pH scale is used to describe the acidity of a solution; the pK a is characteristic of a particular compound

ORGANIC ACIDS AND BASES The most common organic acids are carboxylic acids – Compounds have a COOH group – Have pK a values range from about 3-5

Alcohols – Compounds have an OH group – Are much weaker acids than carboxylic acids – With pK a values close to 16

Water can behave both as an acid and as a base An alcohol behaves similarly

A protonated compounds has gain an additional proton – Very strong acids

HOW TO DETERMINE THE POSITION OF EQUILIBRIUM Strong Acids / Bases React to Form Weak Acids / Bases Compare the pK a values of the acids

HOW THE STRUCTURE OF AN ACID AFFECTS ITS pK a Two factors that affect the stability of a base are its size and its electronegativity When atoms are similar in size, the strongest acid will have its hydrogen attached to the most electronegative atom.

When atoms are very different in size, the strongest acid will have its hydrogen attached to the largest atom.

HOW pH AFFECTS THE STRUCTURE OF AN ORGANIC COMPOUND Whether an acid will lose a proton in an aqueous solution depends on both the pK a of the acid and the pH of the solution. pK a > pH; acidic form (with its proton) pK a = pH; acidic form = basic form pK a < pH; basic form (without its proton)

Physiological pH (pH=7.3)

BUFFER SOLUTIONS A solution containing a weak acid (HA) and its conjugated base (A - ) is called a buffer solution. A buffer solution will maintain nearly constant pH when small amounts of acid or base are added to it

LEWIS ACIDS AND BASES Lewis acid: – Accepts a share in an electron pair – non-proton-donating acid (AlCl 3 ) Lewis base: – donates a share in an electron pair – all bases are Lewis bases