Physical Properties of Organic Compounds

L31-1

SCHWAN LECTURE 31

CHEM*1040

Last meeting: Lecture 30

• Stereoisomerism notes: 30-36 JA 494-8
• structural isomers
• stereoisomers
• chirality and optical rotation

Today:notes pp 39-50

physical properties

intermolecular forces

organic reactions

reactions and their intermedates
Physical properties of Organic compounds

Recall the three main types

1. London or van der Waals forces, induced polarity , due to masses of electrons

2. dipole-dipole interactions

3. H-bonding

and also electrostatic forces for ionic substances

Some functional groups can give us examples

-alkanes have

-for organic halides C-X bond is polar; extent depends on X.

Despite this, boiling points increase in the series RH < RF < RCl < RBr < RI,

For alcohols, O is quite electronegative and H is not very electronegative

considering H-bonding strength,

never do H-bonding with C-H bonds

for carboxylic acids, dimers may forms due to H-bonding

-H-bonding gives the liquids

-H-bonding to water

Complementary to the table on pp. 41 and 42

Consider the following trend

Water solubility

“LIKE DISSOLVES LIKE“

look for common functional groups in both solute and solvent

H-bonding is best

dipole-dipole interactions follow

Chemical Properties Reactions may be

1. ionic, where one reactive partner offers electrons to another, which is willing to accept them.

That receiving the electrons is the

that offering the electrons is the

electrons are attracted to electron deficient or in the extreme, positively charged atoms.

2. free radical and involve neutral species that possess single unpaired electrons

Reaction (Reactive) intermediates

Reactions usually involve some reaction intermediates: either

free radicals, anions or cations

These intermediates

For organic chemistry, these intermediate may be:

Considering the stability of cations and radicals:

Reactions of Alkanes

Free radical halogenation

general reaction:

X = Cl or Br

for bromination of propane:

for radical stability 3º > 2º > 1º

so for the bromination of

Reactions of Alkenes and Alkynes

Addition reactions

The bond of an alkene or alkyne can act like a nucleophile and can react with H+, which acts as an electrophile

and then depending on how the acid was presented , a nucleophile attaches itself to the carbocation

When there is a choice for two different modes, follow the pathway with the more substituted cation: