Ch. 10: Alkanes Chem 20 El Camino College

Organic Chemistry More than 90% of compounds are organic compounds. For pronunciation of organic compound names go to www.merriam-webster.com/dictionary www.howjsay.com

Organic Chemistry Organic chemistry covers compounds made of carbon and hydrogen Other elements, such as O, N, S and Cl may be present

Organic Chemistry Organic compounds They are mostly covalently bonded molecules Usually low melting points Usually low boiling points They are usually not soluble in water, unless a polar group is present

Organic Chemistry Inorganic compounds They are mostly ionic compounds, some are covalent Usually high melting points Usually high boiling points They are usually soluble in water.

ALKANES Remember that carbon has 4 bonds and is often tetrahedral. Wedge formula: Solid wedge represents bond coming forward. Broken wedge represents bond going to the back. Ordinary line represents bond on the plane

Lewis Structures Each bonding pair is represented by a dash. Sometimes we draw long molecules with straight lines, but actually they are not flat

Alkanes Alkanes are a class of hydrocarbons in which the atoms are connected only by single bonds. The general formula for open-chain alkanes is Cn H2n+2 .

Alkanes CH4 methane (1C) CH3CH3 ethane (2C) CH3CH2CH3 propane (3C) CH3CH2CH2CH3 butane (4C) CH3CH2CH2CH2CH3 pentane (5C) CH3CH2CH2CH2CH2CH3 hexane (6C) CH3CH2CH2CH2CH2CH2CH3 heptane (7C) CH3CH2CH2CH2CH2CH2CH2CH3 octane (8C) CH3CH2CH2CH2CH2CH2CH2CH2CH3 nonane (9C) CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 decane (10C)

Drawing Formulas In expanded formulas, every bond is shown In condensed formulas, carbons are shown with the correct number of hydrogen atoms, but not every bond is shown In alkane, C will always have 4 bonds, H will always have 1 bond

Drawing Formulas

Drawing Formulas Hexane has six carbons. Draw expanded and condensed formulas for hexane. (Note: make sure every carbon has 4 bonds)

Drawing Formulas Note--the chains in formulas may not be shown as a straight line. Ex. What compounds are these? butane heptane

Skeletal (Geometric)Formula (Stick structure) Skeletal formulas contain zigzag lines Every corner and every end represents a carbon H atoms are filled in mentally Butane: Hexane

Structural Isomers Isomers have the same chemical formula, but atoms are attached differently 2 different isomers have different properties Are these isomers, or the same molecule? isomers same molecule

Stereoisomers In stereoismers atoms are attached to each other in the same way But they are different in the way atoms are oriented in space Chiral center is a carbon atom to which 4 different groups are attached.

Fisher projection A cross represents a chiral center. Vertical lines represent bonds going away to the back Horizontal lines represent bond coming forward

Cycloalkanes Cycloalkanes have the carbons connected in a “ring” Use cyclo in the name Ex. Condensed formula for cyclohexane Draw a geometric formula for cyclopropane. What is the chemical formula? C3H6

Substituents Alkanes can have attachments Common attachment names: CH3- methyl CH3CH2- ethyl CH3CH2CH2- propyl F-, Cl-, Br-, I- fluoro, chloro, bromo, iodo isopropyl

Alkanes with Substituents 1. Write the name of the longest continuous carbon chain The longest chain has 5 carbons: pentane

Alkanes with Substituents 2. Number the carbon chain from the end nearer a substituent 3. Give the location and name of the substituent. Use a hyphen after the number 2-methylpentane

Alkanes with Substituents Name these 2-chloropentane 3-chloropentane

Alkanes with Substituents Name these 2-bromopropane 3-methylheptane

Alkanes with Substituents Name these, write the formula 4-ethylnonane C11H24 1-bromohexane C6H13Br 3-methylnonane C10H22

Alkanes with Substituents Draw the skeletal formula Draw the expanded formula 2-bromobutane 1-chlorodecane 1-iodopropane cyclobutane

Alkanes with Substituents Name these, write the formula 2-fluorohexane C6H13F cyclopentane C5H10 4-propylheptane C10H22

Alkanes with Substituents 4. Name substituents in alphabetical order 2-bromo-1-iodohexane Name this 3-bromo-2-methylpentane

Alkanes with Substituents Name these 1-bromo-2-chlorobutane 2-chloro-1-fluorobutane 1-bromo-1-fluoro-2-methylpropane

5. Use prefixes like di-, tri-, tetra- for more than one copy of a substituent Every substituent must have its own number Prefixes are not part of alphabetical order.

2,3-dimethylbutane 2,2-dibromobutane 1,2,2-trichlorobutane

6. When there are 2 or more substituents, the main chain is numbered to give the lowest set of numbers Which is correct: 1,5-dibromo-6-chloro-5-methylhexane or 2,6-dibromo-1-chloro-2-methylhexane?

1,2-dibromo-3-methylbutane 1,2-dibromobutane 3-bromo-2-fluoropentane

7. When a single substituent is attached to a cycloalkane, no number is needed. chlorocyclohexane Write the name and chemical formula: ethylcyclobutane C6H12

Draw these ethane 2-methylpropane bromocyclopentane 1,4-dichloro-2-methylbutane 1,1,2,3-tetrabromopropane

Properties, Uses Alkanes are nonpolar, so they’re insoluble in water Alkanes are less dense than water (they float on water) Common alkanes: methane (natural gas), propane (bbq fuel), butane (lighter fuel), octane (fuel) Alkane mixtures also form gasoline, mineral oil, and vaseline.

Combustion The burning of methane in a Bunsen burner is an example of combustion of an alkane alkane + O2 ® CO2 + H2O + energy Write a balanced equation for the combustion of methane gas _____(g) + O2(g) ® CO2(g) + H2O(g) CH4 2 2

Compound Types Alkenes (contain C=C) Alkynes (contain CºC) Alcohols (contain -OH) Ethers (contain C-O-C) Aldehydes (contain H-C=O) Ketones (contain C=O) Carboxylic acids (contain HO-C=O) Esters (contain RO-C=O) Amines (contain N).

Un-Numbered 10.11a

Un-Numbered 10.12a

Un-Numbered 10.12b

Un-Numbered 10.13a

Un-Numbered 10.13b

Un-Numbered 10.14

Un-Numbered 10.15a

Un-Numbered 10.15b

Un-Numbered 10.16

What is the compoud type? ester alkene carboxylic acid ketone aldehyde amine alkane

Substitution Reactions Your next organic reactions will be on haloalkanes (alkanes with a halogen atom substituent) In substitution reactions, one halogen will be substituted for another halogen CH3Br + Cl- ® CH3Cl + Br-

Draw Products, Name the Organic Product chloroethane

Draw Products, Name the Organic Product 2-chloro-2-methylpropane

Name These bromoethane bromoethane 1,1-dibromoethane 1,2-dibromoethane 1,1,2-tribromoethane

Name These 2-bromopropane 2-bromo-2-methylpropane 1,2-dibromo-2-methylpropane 1,1,1,2-tetrabromo-2-methylpropane

Draw Products, Name the Organic Product bromocyclohexane