CH. 2 Families of Carbon Compounds Lecture

Alkane

carbon and hydrogen single bonds

Alkene

carbon-carbon double bond

Alkyne

carbon-carbon triple bond

Arene/ Aromatic

six membered ring with alternating double and sing bonds

• Each carbon is sp² hybridized

• Phenyl group

• benzyl group

Phenyl group

benzene ring attached to another group

Benzyl group

phenyl and methylene (-CH2)

Polar Covalent Bonds

• formed from atoms with different electronegativities

• They have a dipole

• Unit for dipole moment is debye (μ)

Polar and Nonpolar

• Polar molecules have a dipole moment

• Nonpolar molecules have no net dipole moment (but the bonds can be polar)

• Cis/ trans isomers have different dipole moments

Types of Carbons

1) Primary (1^o)- carbon attached to one other carbon

2) Secondary (2^o)- carbon attached to two other carbons

3) Tertiary (3^o)- carbon attached to three other carbons

4) Quaternary (4^o)- carbon attached to four other carbons

Alkyl Halides

a carbon bonded to a halogen like Cl, Br, I, or F

• The carbon attached to halogen needs to be sp³

Alcohol

contains a (-OH) group (a hydroxyl group)

Amine

contains nitrogen usually bonded to a carbon group or hydrogen

• Nitrogen is sp³

• Tetrahedral arrangement of electrons

• Trigonal pyramidal molecular geometry

Types of Amines

based on the number of carbon groups attached tot the nitrogen

Nitrile

carbon triple bonded to nitrogen

Nitro

has a (-NO₂) group

Ether

an oxygen atom between two carbons

Acid chloride

carbonyl (C=O) bonded to a chlorine atom

Aldehyde

a carbonyl (C=O) bonded to a hydrogen

Ketone

a carbonyl (C=O) bonded to two carbons

Carboxylic acid

a carbonyl (C=O) bonded to an -OH

Ester

a carbonyl bonded to carbon and an oxygen with a carbon

Amide

a carbonyl bonded to an amine

Type of Amides

based on carbon groups attached to nitrogen

Carboxylic Acid Anhydride

contains two carbonyls linked through an oxygen

Functional Groups

• most functional groups have a dipole

  • Can be represented by arrows

  • Can be represented by delta symbol
    

Physical Properties

• can help identify substance

  • Melting point

  • boiling point

  • solubility

Ion-Ion Intermolecular Force

• Holds ionic compounds together

• Very strong

• Ionic compounds have high melting point

Ex. NaCl

Dipole-Dipole Intermolecular Force

• Permanent dipole moments

• Forces hold most organic compounds together

• Forces b/w polar compounds

• Weak force, easy to break

Ex. Acetone, CH₃COCH₃

Hydrogen Bonds

• Very strong dipole-dipole interaction

• Occurs b/w O, N, or F (strong electronegative atoms) and a hydrogen attached to an O, N, or F

• Weaker than ordinary covalent bonds but much stronger than dipole-dipole forces

• Takes more energy to break H-bonds

Hydrogen Bonds

• compounds that can form H-bonds have higher boiling point than compounds that cannot

• The more -OH groups, the higher the boiling point in compound with similar molecular weight and number of carbon

Hydrogen Bonds

• Branching decreases the boiling point and melting point of compound

  • Less surface area and more compact structures lead to fewer attractions

• Symmetrical alcohols do not follow the general rule above

  • They have abnormally high melting point

Dispersion Forces

• induced dipole or van de Waals or London forces

• Temporary dipole results from the electrons in atoms moving within the atom

• Molecules have an induced (+) and (-) end

• Attractive forces b/w nonpolar molecules

What are the 2 important factors of determining the magnitude of dispersion forces?

1) Polarizability of electrons- how easily the electrons respond to a changing electric field

• The larger the atom, the farther away its electrons are from the nucleus, the more polarizability (Cl<Br<I)

• Atoms with unshared electrons are easily polarized compared to atoms with all bonding electrons.

2) Surface area- the larger the surface area, the larger the overall attraction between molecules

Surface Area

the larger the surface area, the larger the the overall attraction b/w molecules

Boiling Points

The temperature at which the vapor pressure of the liquid equals the vapor pressure of the atmosphere

• boiling point is pressure dependent: decreasing the pressure, decreases the boiling point

• Nonpolar compounds with weak forces usually boil at low temp.

• Heavier molecules need more energy to boil (surface area is larger and so are the dispersion forces)

Solubility

• “like dissolves like”

• Nonpolar compounds dissolve in nonpolar solvents

• Water hydrates or solvates ionic compounds

• Alkyl groups are hydrophobic (water fearing)

• -OH groups are hydrophilic (water loving)

• Oil is not soluble in water- it is all hydrocarbon

• The longer the hydrocarbon chain, the less water soluble

  • after the 5 carbon, compound becomes less soluble

Physical Properties of Alkanes

• Boiling point of unbranched alkanes increase with molecular weight

• Branching decreases surface area and decreases boiling point

• Density: alkanes have very low densities and float on water

• Alkanes are insoluble in water

Infrared Spectroscopy

can give you structural information about a compound

• what FUNCTIONAL GROUP are in a compound

• Type of electromagnetic radiation

  • Has lower energy than visible light

Infrared Spectroscopy

• all molecules have molecular vibrations

• when infrared radiation is absorbed, the frequency of the radiation matches the frequency of the molecular vibration

IR Spectrum

• 3000-3500: C-H, O-H, N-H

• 2200: C≡N; C≡C

• 1600-1800: C=O; C=N; C=C

Alkane

• C-C

• 2850-2960

• medium

Alkanyl

• C-H

• Less an 3000

Alkene

• C=C

• 1640-1680

• Medium

Alkenyl

• =C-H

• 3020-3100

• Medium

Alkyne

• C≡C

• 2100-2260

• Medium

Alkenyl

• ≡C-H

• 3300

• Strong

Alcohol

• O-H

• 3400-3650

• Strong, broad

Arene

• C-H

• 3030

• weak

Aromatic Ring

• 1660-2000

• weak

Amine

• N-H

• 3300-3500

• medium

Carbonyl Compound

• C=O

• 1670-1780

• Strong

Nitrile

• C≡N

• 2210-2260

• medium

Aldehyde

• Fermi doublet

• about 2800-2810

• only have a fermi doublet

Double bond

1500-2000

Triple Bond

2000-2500