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Organic Chemistry Fundamentals: Metric Conversions, Polyatomic Ions, Molecular Geometry, and Functional Groups

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Metric Unit Conversions and Avogadro's Number

Metric Unit Conversions

Understanding metric unit conversions is essential for quantitative work in chemistry. The following table summarizes common conversions used in laboratory and theoretical calculations.

Conversion

Equivalent

1 L

1,000 mL / 1,000 cm3

1 g

1,000 mg

1,000 g

1 kg

2.2 lbs

1 kg

1 mile

1.60934 km

Avogadro's Number

Avogadro's Number is a fundamental constant in chemistry, representing the number of particles (atoms, molecules, ions) in one mole of a substance.

  • 1 mole = molecules/atoms

Mnemonic: OIL RIG

OIL RIG is a mnemonic for remembering oxidation and reduction:

  • Oxidation Is Loss (of electrons)

  • Reduction Is Gain (of electrons)

Polyatomic Ions

Common Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms covalently bonded, carrying a net charge. Recognizing these ions is crucial for naming compounds and predicting chemical behavior.

Ion Name

Formula

Charge

Ammonium

NH4+

+1

Nitrate

NO3-

-1

Sulfate

SO42-

-2

Phosphate

PO43-

-3

Hydroxide

OH-

-1

Carbonate

CO32-

-2

Acetate

C2H3O2-

-1

Chlorate

ClO3-

-1

Permanganate

MnO4-

-1

Chromate

CrO42-

-2

*Additional info: Table entries inferred from standard polyatomic ions list in general chemistry.*

Molecular Geometry and Bond Angles

VSEPR Theory and Molecular Shapes

The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the shapes of molecules based on the number of electron groups around the central atom. The arrangement minimizes repulsion between electron pairs.

"Groups" on Center Atom

Bonded Atoms

Lone Pairs

Molecular Shape

Bond Angle

No Center Atom

2

0

Linear

180°

2

2

0

Linear

180°

3

3

0

Trigonal planar

120°

3

2

1

Bent

120°

4

4

0

Tetrahedral

109.5°

4

3

1

Trigonal pyramidal

109.5°

4

2

2

Bent

109.5°

  • Linear: All atoms in a straight line, bond angle 180°.

  • Trigonal planar: Three atoms around a central atom in one plane, bond angle 120°.

  • Tetrahedral: Four atoms around a central atom, bond angle 109.5°.

  • Bent: Central atom with lone pairs, resulting in a bent shape.

  • Trigonal pyramidal: Three atoms and one lone pair around the central atom.

Organic Functional Groups and Classification

Overview of Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for characteristic chemical reactions. Recognizing these groups is fundamental in organic chemistry.

Class

Structure

Description

Alkane

All single bonds between carbon and hydrogen atoms

"Chain" structure

Haloalkane

Alkane with one or more halogen group elements

Halogen substitution

Cycloalkane

Cyclic alkane

"Circle" structure

Alkene

At least one double bond

"Chain" with double bond

Cycloalkene

Cyclic alkene

"Circle" with double bond

Alkyne

At least one triple bond

"Chain" with triple bond

Aromatic

Cyclic carbon molecule with double bonds every other bond

Benzene ring structure

Alcohol

Hydroxyl group (OH)

R-OH

Phenol

Aromatic ring with hydroxyl group

Benzene ring with OH

Thiol

Sulfur and hydrogen group

R-SH

Ether

Oxygen with two carbon groups attached

R-O-R'

Amine

Nitrogen bonded to the molecule

R-NH2, R-NHR', R-NR'2

Aldehyde

Carbonyl group with at least one hydrogen

R-CHO

Ketone

Carbonyl group with two carbon groups

R-CO-R'

Carboxylic Acid

Carbonyl group with hydroxyl group

R-COOH

Ester

Carbonyl group with an oxygen

R-COO-R'

Amide

Carbonyl group with an amine group

R-CONH2

  • Alkane: Saturated hydrocarbons with only single bonds.

  • Alkene: Unsaturated hydrocarbons with at least one double bond.

  • Alkyne: Unsaturated hydrocarbons with at least one triple bond.

  • Aromatic: Cyclic, planar molecules with delocalized electrons (e.g., benzene).

  • Alcohol: Organic compounds with a hydroxyl group attached to a carbon atom.

  • Phenol: Hydroxyl group attached to an aromatic ring.

  • Thiol: Sulfhydryl group attached to a carbon atom.

  • Ether: Oxygen atom connected to two alkyl or aryl groups.

  • Amine: Nitrogen atom attached to one or more alkyl or aryl groups.

  • Aldehyde: Carbonyl group bonded to at least one hydrogen.

  • Ketone: Carbonyl group bonded to two carbon atoms.

  • Carboxylic Acid: Carbonyl group bonded to a hydroxyl group.

  • Ester: Carbonyl group bonded to an oxygen atom, which is bonded to another carbon.

  • Amide: Carbonyl group bonded to a nitrogen atom.

Example: Identifying Functional Groups

  • Ethanol (C2H5OH): Contains an alcohol functional group.

  • Acetone (CH3COCH3): Contains a ketone functional group.

  • Acetic acid (CH3COOH): Contains a carboxylic acid functional group.

*Additional info: Functional group definitions and examples expanded for clarity.*

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