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Essentials of Organic Chemistry
Chemistry 304
Thomas J. Wiese, Ph.D.
Associate Professor of Chemistry
Fort Hays State University
Course Overview
Ch. 1-9, 18?
The way to study:• scan assigned reading material before class• listen during class and take notes• read assigned material (SQ3R) and supplement class
notes• review the weeks notes every weekend• begin good study habits early!• pay attention to details I point out
Compound vs. molecule
Compound- atoms of two or more elements bonded together
Molecule has two meanings
• Atoms of the same element bonded together
• A single compound moiety
Atomic Structure
A nucleus containing protons and neutrons, surrounded by a cloud of electrons
s-electrons
p-electrons (px, py, and pz)
(d-electrons and f-electrons)
Electron Configurations
Two electrons (e–) per orbitalPrinciple energy levels and the Aufbau principle
1 contains only s e–
2 contains s and p e–
3 contains s, p and d e–
4 contains s, p, d and f e–
Spin-pair ruleHunds rule
Bonds
Ionic bond- electrostatic interaction when metal and nonmetal interact (NaCl as an example)
Covalent bond-A chemical bond that involves sharing of electron pairs (not all same)
Two shared electrons = 1 bond (H2)
Molecular Properties
Ionic compounds
solid
high mp/bp
conductors
vs. Covalent compounds
solid or liquid or gas
low mp/bp
insulators
Other Bond Issues
Polar covalent bond (O—H)
Double bond (O2) and triple bond (N2)
Coordinate covalent bond (NH4+ formation)
Charge and Formal Charge
• There is a formal charge for each atom of a compound
-e shared
theof halfminus
electrons
unsharedminus
number
groupcharge Formal
Review Questions
• Are the following bonds polar or nonpolar?
C-C
C-H
C-O
C-N
C hart I. E le c tro ne ga t iv it ies o f Se lec te d E le m e n ts
H2 .2 1
H e—
L i0 .9 8
B e1 .5 7
B2 .0 4
C2 .5 5
N3 .0 4
O3 . 4 4
F3 .9 8
N e—
N a0 .9 3
M g1 .3 1
A l1 .6 1
S i1 .9 0
P2 .1 9
S2 . 5 8
C l3 .1 6
A r—
K0 .8 2
C a1 .0 0
G a1 .8 1
G e2 .0 1
A s2 .1 8
S e2 . 5 5
B r2 .9 6
K r—
R b0 .8 2
S r0 .9 5
In1 .7 8
S n1 .9 6
S b2 .0 5
T e2 . 1 0
I2 .6 6
X e—What are the formal charges
for the carbonate ion, CO32-?
6
Forces between MoleculesI. London Forces
• all particles have London forces
Ar.
.
Ne Ne
• larger particles have larger London forces
• only force between noble gases and nonpolar compounds• about 1/1000 as strong as a covalent bond
7
Forces between MoleculesII. Dipole-Dipole Interactions
• different from London forces only in permanence
• somewhat stronger than London forces because permanent
• occurs in all polar molecules
• weaker than ionic bond because only + or
C
O
H H
.
.
8
Forces between MoleculesIII. Hydrogen Bonds
• rare• occur between one H
which is covalently bonded to an N, O, or F atom and a second N, O, or F atom
• strongest of three intermolecular forces
OHH
OHH
OHH
OHH
OHH
.
.
Carbon
• Atomic structure– 6 p
– Predominately 6 neutrons
– 6 e–
C• group IVA–4 valence electrons
–oxidation state “±4”
–form 4 bonds in reactions
–tetrahedral
Atomic Orbitals
electron configuration of C
1s2,2s2,2p2
We might expect C to form two bonds ( the 2 unpaired p electrons)
We know that C forms 4 bonds We might expect that CH4 would have 1 s-s
bonds and 3 s-p bonds.
We know that all C–H bonds are equivalent
Hybrid Atomic Orbitals
Hybrid atomic orbitals is a theory used to reconcile the discrepancy between what atomic orbital theory predicts, and what is seen experimentally.
• Fig 1.12: C has 4 sp3 hybrid orbitals– called sigma bonds
• pi bonds: sp2 hybrid orbitals
Hybrid Atomic Orbitals
hybrid bonding shape rotation bond
sp3() head-head tetrahedral free single
sp2 () sideways triangular rigid double
sp () sideways linear rigid triple
There are a Huge Number of Organic Molecules
• 100 new ones described every week
• It is estimated that there could be 5 1020 different organic molecules
How Can So Many Molecules be Made From So Few Elements?
• different number of C atoms
• Functional groups (later)
• Isomers– iso means…
Empirical formula- C6H14 (molecular formula)
Structural formula
Drawing Molecules
As you can see already, drawing all these C-H bonds is tedious. We will use shortcuts most of the time.
Condensed formula
Line formula
Drawing Molecules on Paper Does not Show the 3-Dimensional Shape
The geometry around each C atom is tetrahedral (sp3 hybrid)
Hydrocarbons
Hydrocarbon- Compounds which contain only carbon and hydrogen.
Alkanes
Alkenes
Alkynes
Cycloalkanes
(Aromatics)
Alkanes
meth- 1 carbon
eth- 2 carbons
prop- 3 carbons
but- 4 carbons
pent- 5 carbons
hex- 6 carbons
hept- 7 carbons
oct- 8 carbons
non- 9 carbons
dec- 10 carbons
IUPAC Nomenclature1. Find the longest continuous carbon chain and use the name for the
alkane with that number of carbon atoms.
2. Number the carbons in the longest continuous carbon chain from the end nearer the first R group.
3. Identify R groups by name.
4. Identify by number the carbon atom in the chain to which each substituent bonds. If the same substituent occurs more than once, identify each carbon number for that substituent, separate the numbers to commas, and use the appropriate prefix to identify how many occur in the compound.
5. Name the compound by listing the substituents preceded by a number and a hyphen, followed by the base name for the C chain. If more than one type R group, arrange in alphabetical order, ignoring prefixes except iso- and cyclo-. Connect all numbers and prefixes by hyphens.
R-groups by name
CH2CH2H3 propyl
CH
CH3
CH3
isopropyl
CH2CH2CHCH3
CH3
isopentyl
CH2CHCH2CH3
CH3
secpentyl
CH2CCH3
CH3
CH3
neopentyl(tertpentyl)
.
.
Cycloalkanes
Whether the ring or chain is considered the parent compound depends on which is larger.
CH3CH2
.
.
Functional Groups
Functional group- An atom or group of atoms that imparts on a molecule a distinctive chemistry
1. Alkane- not considered a functional group
2. Alkyl halide
3. Alkene
4. Alkyne
Alkanes
Only sigma bonds in molecules
General formula CnH2n+2
Molecular formula
Structural formula
Condensed formula
Isomers- same formula, different structure
functional isomers
structural isomers
Conformation of Molecules
• Important because of free rotation about the -bond
• Eclipsed-
• Staggered-
• Important because of size of groups (can overlap)
Practice Conformation Problems
• Draw “all possible” Newman projections for the compound CH3CH2CH2CH3 (butane)
.
.
H
CH3H
CH3
H H
.
.
H
CH3H
H
H CH3
CH3
HH
CH3
H H
H
HCH3
CH3
H H
Practice Conformation Problems
• What would the most stable conformation of the following molecule be?
CH3CH2 CH2CH3
CH3CH2CH2CH3
diequitorial
CH2CH3
CH3CH2
diaxial
axial-equitorial
CH2CH3
CH2CH3
CH3CH2 CH2CH3
boat