Essentials of Organic Chemistry

Chemistry 304

Thomas J. Wiese, Ph.D.

Associate Professor of Chemistry

Fort Hays State University

Introduction

• Roll Call

• Syllabus

• Tests and Grading

• Approximate grading scale: 90-80-70-60

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

Introduction to Organic Chemistry

(Review of Freshman Chemistry)

Element

Element- pure substance composed of only one type of atom

H vs. He vs. Unh

Atom

Atom- the smallest particle of matter

Composed of protons, neutrons and electrons

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

6/9/04

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-?

Intermolecular Forces

London forces (AKA van der Waals)

Dipole-dipole interactions

Hydrogen bond

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

.

.

6/10/04

Solubility

• “Like dissolves like”

• Solvent-

• Solute-

• 4 C

Shapes of Molecules

• Linear

• Bent

• Pyramidal

• Tetrahedral

• Triangular

• others

Organic Chemistry

Organic chemistry- the chemistry of carbon-containing compounds

Forms of Elemental Carbon

• Graphite• Diamond• Buckminsterfullerene -

Nobel prize 1996• “Amorphous”

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

6/14/04

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

Nomenclature

• Primary

• Secondary

• Tertiary

• Quaternary

6/15/04

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

6/16/04

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

Physical Properties of Alkanes

1. Solubility

2. mp/bp

3. Density