CH. 4 Nomenclature and Conformations of Alkanes and Cycloalkanes

Cycolalkanes

rings with only single bonds

Shapes of Alkanes

• Alkanes contains sp³ hybridized carbons and are tetrahedral

• straight chain or unbranched alkanes

  • normal or n-alkanes

Branched Alkanes

Rules for Naming #1

locate the parent (longest) chain

• It is not always in a straight line

Rules for Naming #2

Number the atoms in the main chain; start at the end closest to the branching

Rules for Naming #3

Identify and number the substituents (groups)

Rules for Naming #4

two or more substituents: list in alphabetical order

Rules for Naming #5

substituents are the same carbon: use number twice

Rules for Naming #6

if there are multiple substituents that are the same use the prefix di, tri, tetra, etc.

Rules for Naming #7

if there are two chains of equal length, choose the one with the larger number for branching

Rules for Naming #8

when branching occurs at equal distance from either end, choose the name that gives the lower number at the point of difference

Isopropyl group (iPr)

• non-systematic

sec-Butyl group (sec-Bu)

• non-systematic

Isobutyl group

• non-systematic

Tertiary-butyl group (t-Bu or tert-Bu)

• non-systematic

Classification of Hydrogen Atoms

• 1^o hydrogen is attached to a 1^o carbon

• 2^o hydrogen is attached to 2^o carbon

• 3^o hydrogen is attached to 3^o

Naming Alkyl Halides

• drop the “-ine” and add “-o”

  • Chlorine→ chloro

  • Bromine→ bromo

Naming Alcohols

• drop “-e” and add “-ol” suffix

Glycols and diols (IUPAC)

alcohols with two hydroxyl groups

Naming Cycloalkanes Rule #1

• Find the parent chain

• If the number of carbon atoms in the ring is equal to or greater than the number of carbons in the substituents, the compound is named as an alkyl-substituted cycloalkane

Naming Cycloalkanes Rule #2

• Number the substituents

• Start #1 at the substituent that gives the lowest possible number then put in alphabetical order

Naming Cycloalkanes Rule #3

• If more than one ring is attached, name as a cycloalkyl-substituted alkane

Bicyclic Compounds

• fused ring structures

• With substituents, start numbering at bridgehead then go around the largest ring first

Naming Alkenes and Cycloalkenes Rules #1 and #2

• #1: find the longest chain that contains the double bond, drop -ane and use the -ene suffix

• #2: both carbons of the double bond must be included in the numbering

Naming Alkenes and Cycloalkenes Rule #3

• number at the end closest to the double bond; substituents are not the highest priority

• If equal distance from either end, start at the end closest to branching

Naming Alkenes and Cycloalkenes Rule #4

• For cycloalkenes: the double bond is #1 and #2 then number the rest of the substituents giving the lowest number possible

Naming Alkenes and Cycloalkenes Rule #5

• For double bond and alcohol, name as a alcohol

Naming Alkenes and Cycloalkenes Rule #6

• alkenes can be groups on other molecules

Naming Alkenes and Cycloalkenes Rule #7

• Cis- and trans- prefix can be used when you have two substituents (not hydrogen) on opposite end of the double bond

Naming Alkynes

• drop -ane and use the -yne suffix

• Named as alcohols if they contain -OH

Terminal alkyne

• known as a mono-substituted acetylene

Physical Properties of Alkanes

• Boiling point of unbranched alkanes increase with the molecular weight

• Branching decreases surface area and decrease boing point

• Density- alkanes and cycloalkanes have very low densities and float on water

• Alkanes and cycloalkanes are insoluble in water

Sigma Bond and Bond Rotation

• Groups bonded by sigma bonds have free rotation about the bond

• The temporary shape is known as conformation

• Each possible structure is a conformer

• The Newman projection and Sawhorse formulas are useful for looking at conformations