FUNCTIONAL GROUPS

……..an atom or bond……… or a group of atoms or bonds that is attached to one or more C atoms that has a……..

… characteristic chemical behavior

What is a Functional Group (FG) ?

CH3 C OH

O

This is a functional group. It isnamed the carboxy group.

Functional Groups and Reactivity

FGs change reactivity and physical properties of a molecule

Reactivity is the rate at which a molecule isconverted to product or its behavior toward specific reagents.

Functional Groups

Functional Groups

FGs Also Change a Molecule’s Physical Properties

FGs Also Change a Molecule’s Physical Properties

Property Ethane(C2H6) Ethanol (EtOH)

b.p. -89 C 78 C

Soluble in water?

Rxn w H3PO4/∆?

Identify the Functional Groups

The C-O Group

The C=C Group

The C=O Group

The Phenyl Group

Functional Groups

Functional group determines all of the following properties of a molecule :

bonding & shape

type & strength of intermolecular forces

physical properties

nomenclature

chemical reactivity

Intermolecular Forces (I.F.)

Intermolecular Forces-ionic

van der Waals forces

dipole-dipole interactions

hydrogen bonding

Intermolecular Forces-non-ionic

Van der Waals Forces

Van der Waals Forces

• Polarizability is a measure of how the electron cloud around an atom responds to changes in its electronic environment.

Dipole-Dipole Interactions

Hydrogen Bonding

Intermolecular Forces & Physical Properties

Physical Properties—Boiling Point

• The stronger the intermolecular forces, the higher the boiling point.

• For compounds with approximately the same molecular weight:

Physical Properties—Boiling Point

For two compounds with similar functional groups:

• The larger the surface area, the higher the boiling point.

• The more polarizable the atoms, the higher the boiling point.

Physical Properties—Boiling Point

Liquids having different boiling points can be separated in the laboratory using a distillation apparatus, shown in Figure 3.4.

Physical Properties—Boiling Point

Introduction to Organic Molecules and Functional Groups

• The melting point is the temperature at which a solid is converted to its liquid phase.

• In melting, energy is needed to overcome the attractive forces in the more ordered crystalline solid.

• The stronger the intermolecular forces, the higher the melting point.

• Given the same functional group, the more symmetrical the compound, the higher the melting point.

Physical Properties—Melting Point

Introduction to Organic Molecules and Functional Groups

• Because ionic compounds are held together by extremely strong interactions, they have very high melting points.

• With covalent molecules, the melting point depends upon the identity of the functional group. For compounds of approximately the same molecular weight:

Physical Properties—Melting Point

Introduction to Organic Molecules and Functional Groups

• The trend in melting points of pentane, butanal, and 1-butanol parallels the trend observed in their boiling points.

Physical Properties—Melting Point

Introduction to Organic Molecules and Functional Groups

• Symmetry also plays a role in determining the melting points of compounds having the same functional group and similar molecular weights, but very different shapes.

• A compact symmetrical molecule like neopentane packs well into a crystalline lattice whereas isopentane, which has a CH3 group dangling from a four-carbon chain, does not. Thus, neopentane has a much higher melting point.

Physical Properties—Melting Point

Introduction to Organic Molecules and Functional Groups

• Solubility is the extent to which a compound, called a solute, dissolves in a liquid, called a solvent.

• In dissolving a compound, the energy needed to break up the interactions between the molecules or ions of the solute comes from new interactions between the solute and the solvent.

Physical Properties—Solubility

Introduction to Organic Molecules and Functional Groups

• Compounds dissolve in solvents having similar kinds of intermolecular forces.

• “Like dissolves like.”

• Polar compounds dissolve in polar solvents. Nonpolar or weakly polar compounds dissolve in nonpolar or weakly polar solvents.

•Water and organic solvents are two different kinds of solvents. Water is very polar since it is capable of hydrogen bonding with a solute. Many organic solvents are either nonpolar, like carbon tetrachloride (CCl4) and hexane [CH3(CH2)4CH3], or weakly polar, like diethyl ether (CH3CH2OCH2CH3).

•Most ionic compounds are soluble in water, but insoluble in organic solvents.

Physical Properties—Solubility

Introduction to Organic Molecules and Functional Groups

• An organic compound is water soluble only if it contains one polar functional group capable of hydrogen bonding with the solvent for every five C atoms it contains. For example, compare the solubility of butane and acetone in H2O and CCl4.

Physical Properties—Solubility

Introduction to Organic Molecules and Functional Groups

• Since butane and acetone are both organic compounds having a C—C and C—H backbone, they are soluble in the organic solvent CCl4. Butane, which is nonpolar, is insoluble in H2O. Acetone is soluble in H2O because it contains only three C atoms and its O atom can hydrogen bond with an H atom of H2O.

Physical Properties—Solubility

Introduction to Organic Molecules and Functional Groups

• To dissolve an ionic compound, the strong ion-ion interactions must be replaced by many weaker ion-dipole interactions.

Physical Properties—Solubility

Introduction to Organic Molecules and Functional Groups

• The size of an organic molecule with a polar functional group determines its water solubility. A low molecular weight alcohol like ethanol is water soluble since it has a small carbon skeleton of five C atoms), compared to the size of its polar OH group. Cholesterol has 27 carbon atoms and only one OH group. Its carbon skeleton is too large for the OH group to solubilize by hydrogen bonding, so cholesterol is insoluble in water.

Physical Properties—Solubility

Introduction to Organic Molecules and Functional Groups

• The nonpolar part of a molecule that is not attracted to H2O is said to be hydrophobic.

• The polar part of a molecule that can hydrogen bond to H2O is said to be hydrophilic.

• In cholesterol, for example, the hydroxy group is hydrophilic, whereas the carbon skeleton is hydrophobic.

Physical Properties—Solubility

Introduction to Organic Molecules and Functional Groups

Are these molecules water soluble?

Polarity is the basis of micelle formation

Introduction to Organic Molecules and Functional Groups

Application—The Cell Membrane

Transport Across a Cell Membrane: • Polar molecules and ions are transported across cell membranes

encapsulated within molecules called ionophores.• Ionophores are organic molecules that complex cations. They have a

hydrophobic exterior that makes them soluble in the nonpolar interior of the cell membrane, and a central cavity with several oxygens whose lone pairs complex with a given ion.

Introduction to Organic Molecules and Functional Groups

Application—The Cell Membrane

Transport Across a Cell Membrane:

Introduction to Organic Molecules and Functional Groups

Application—The Cell Membrane

Several synthetic ionophores have also been prepared, including one group called crown ethers.

Crown ethers are cyclic ethers containing several oxygen atoms that bind specific cations depending on the size of their cavity.

Application—The Cell Membrane

Introduction to Organic Molecules and Functional Groups

Functional Groups and Reactivity (E.N. atom)

Example of an Electrophilic Alkyl Halide( RX)

Functional Groups and Reactivity (lone pairs)

Functional Groups and Reactivity ( bonds)

Example of a Nucleophilic bond