Organic Chemistry

Hydrocarbons

Organic Chemistry

• The study of the compounds that contain the element carbon

• Are numerous due to the bonding capability of carbon

Carbon

• Is able to form 4 covalent bonds

• can form single, double, or triple covalent bonds

• makes possible a large number of compounds

Organic Compounds

• Extensive in nature

• more numerous than inorganic compounds

Major sources of raw materials from which organic chemicals are obtained

• Petroleum

• coal

• wood

• animal sources

Characteristics of organic compounds

• Generally insoluble in water (are generally nonpolar)

• dissolve in nonpolar solvents (benzene)– organic compounds that are somewhat

polar will dissolve in water

• Are generally nonelectrolytes

• generally low melting points – nonpolar - intermolecular forces weak

• slower reactions than those involving inorganic compounds – have strong covalent bonding within the

molecule

Bonding

• Forms compounds by covalent bonding

• C atom has 4 valence electrons forms 4 covalent bonds

• are spacially directed toward the corners of a regular tetrahedron

• |

• — C —

• |

Can share electrons with other C atoms

2 adjacent C atoms can share 1,2, or 3 pairs of electrons

compounds are molecular in structure covalent bond represent by “ — “

(bond line) represents one pair of shared electrons

Types of formulas

• STRUCTURAL FORMULA– Formula showing bonding

• CONDENSED STRUCTURAL FORMULA– leave out some bonds and/or atoms from

the structural formula

• Page 746

• examples in table– molecular formula– complete structural formula– condensed structural formula– more condensed structural formula– carbon skeleton

Isomers

• Have same molecular formula but different structures

• example

– propanol CH3CH2CHO– acetone CH3COCH3

• both have molecular formula C3H6O

• As the number of atoms in the molecule increases, the possibility of more spatial arrangements increases (more isomers)

Saturated compounds

• Organic compounds in which carbon atoms are bonded by the sharing of a single pair of electrons. Are all single bonds (one pair shared)

• | | | | |

• — C — C — C — C — C —

• | | | | |

Unsaturated compounds

• Contain 2 adjacent carbon atoms bonded by the sharing of more than one pair of electrons

• double bond > C = C <

• triple bond — C = C —

• (add third bond line please)

Hydrocarbons

• Organic compounds that contain only hydrogen and carbon

Homologous series of hydrocarbons

• Groups having related structures and properties

• each member of a series differs from the one before it by a common amount

• As members of a series increase in molecular size, boiling point and freezing point increases due to Van der Waal’s Forces (force that holds nonpolar molecules together)

Alkanes

• Series of saturated hydrocarbons having the general formula:

• CnH2n+2

• also called methane series or paraffin series

• Alkane series begins showing isomerism at butane (C4H10)

• Straight-chain alkanes - contain any number of carbon atoms, one after another, in a chain

• Page 745

• Must memorize the prefixes - tells you how many carbon atoms are in the compounds

METHANE CH4

•

• H

• |

• H — C — H

• |

• H

ETHANE C2H6

•

• H H

• | |

• H — C — C — H

• | |

• H H

PROPANE C3H8

• H H H

• | | |

• H— C — C — C — H

• | | |

• H H H

BUTANE C4H10

• H H H H

• | | | |

• H — C — C — C — C — H

• | | | |

• H H H H

PENTANE C5H12

• H H H H H

• | | | | |

• H — C — C — C — C — C — H

• | | | | |

• H H H H H

• Page 747

• Sample problem 25-1 (done for you)

• Practice problems– change to six and seven carbons

SUBSTITUENTS

• An atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule

• The halogens and groups of atoms including C, H, O, N, S, or P may take the place of a hydrogen atoms

• A hydrocarbon substituent is called an alkyl group can be one carbon or several carbons long

• examples:

• methyl CH3—

• ethyl CH3CH2 —

• propyl CH3CH2CH2

• Alkyl group consists of an alkane with one hydrogen removed

• alkyl groups sometimes called radicals

• Are named by removing the -ane ending from the parent hydrocarbon name and adding -yl

• page 748 Answer red dot question

• Page 748-749

• branched chain alkane - alkane with one or more alkyl groups

• IUPAC SYSTEM FOR NAMING BRANCHED CHAIN ALKANES

• follow in text #1-6

• Page 749 Sample Problem 25-2

• Practice problem 3

• Page 750 Practice Problem 4

• Can also reconstruct the structural formula by following the rules on page 750

• Sample problem 25-3• practice problem 5 • Pg. 751 Practice problem 6

Unsaturated hydrocarbons

• ALKENES

– contain one double bond between adjacent carbons

• page 754 look at structures

• Ethene (ethylene)

• propene (propylene)

• butene

• pentene

• and so on……..

Naming alkenes

• Locate the longest chain that contains the double bond– that is the parent alkene

• use that root name plus ene ending • number the chain so that the

carbons with the double bond get the lowest numbers

• Substituents names the same way as for alkanes

• use a number to indicate the location of the carbon that has the double bond

ALKYNES

• Contain a triple bond between 2 carbons

• not plentiful in nature

• ethyne (acetylene)

• page 753 look at table 25.2

Isomerism

• Structural isomers– Compounds that have the same

molecular formula but different molecular structures

• examples on page 754

• butane and 2-methylpropane

• Have different physical properties (melting point, boiling point) In general, the more highly branched in structure, the lower its boiling point)

• also have different chemical properties

Geometric isomers

• Differ only in the geometry of their substituted groups

• trans configuration - the substituted groups are on the opposite side of the double bond

• Cis configuration - the substituted groups are on the same side of the double bond

• example on pages 754-755

• answer pink question #2

Stereoisomers

• Molecules of the same molecular structure that differ only in the arrangement of the atoms in space.

• Page 755 example

• page 756 samples and practice