Organic chemistry
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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 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
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