An Introduction to Organic Compounds Nomenclature, Physical Properties, and Representation of Structure

Contents of Chapter 2 Nomenclature Structures of Alkyl Halides, Alcohols, Ethers, and Amines Physical Properties Conformations of Alkanes Cycloalkanes

Counting to Ten in Organic 01 = meth Mother 02 = eth Enjoys 03 = prop Peanut 04 = but BUTter 05 = pent PENTagon 06 = hex HEXagon or HEX nut 07 = hept HEPTember (Roman sept is Greek hept) 08 = oct OCTober 09 = non NONember (Roman nov is Greek non) 10 = dec DECember

Alkanes

Primary, Secondary, Tertiary A primary carbon has one other C directly bonded to it. A secondary carbon is directly bonded to two other C’s. A tertiary carbon is directly bonded to three other C’s. Multivalent atoms are 1º, 2º, or 3º by bonding to C’s. Univalent atom or group not really 1º, 2º, or 3º on its own - ID depends on type of carbon it is bonded to.

Nomenclature of Alkyl Substituents There are four alkyl groups that contain four carbons

Nomenclature of Alkyl Substituents The prefix sec- occurs only in sec-butyl

Nomenclature of Alkyl Substituents The prefix tert- can be used with butyl or pentyl (also known as amyl) but not with hexyl

IUPAC Systematic Nomenclature - Alkanes Determine longest continuous chain (i.e. parent hydrocarbon) Cite the name of substituent before the name of the parent hydrocarbon along with the number of the carbon to which it is attached

IUPAC Systematic Nomenclature - Alkanes Number in the direction that gives the lower number for the lowest-numbered substituent. Substituents are listed in alphabetical order – neglecting prefixes such as di- tri- tert- etc.

IUPAC Systematic Nomenclature - Alkanes When both directions yield the same lower number for the lowest numbered substituent, select the direction that yields the lower number for the next lowest numbered substituent

IUPAC Systematic Nomenclature - Alkanes If same substituent numbers are obtained in either direction, number in direction giving lowest number to the first named substituent

IUPAC Systematic Nomenclature - Alkanes If compound has two or more chains of the same length, parent hydrocarbon is chain with greatest number of substituents

IUPAC Systematic Nomenclature - Alkanes Names such as sec-butyl and tert-butyl are acceptable, but systematic substituent names are preferable Numbering of the substituent begins with the carbon attached to the parent hydrocarbon This number together with the substituent name is placed inside parentheses

Nomenclature of Cycloalkanes Cycloalkanes generally are shown as skeletal structures

Nomenclature of Cycloalkanes Ring is the parent hydrocarbon unless the alkyl substituent has more carbons; in that case the substituent becomes the parent hydrocarbon If only one substituent, no need to give it a number

Nomenclature of Cycloalkanes If the ring has 2 substituents, list in alphabetical order and give number 1 to first named group

Nomenclature of Cycloalkanes If there is more than one substituent, list in alphabetical order; one substituent is given the position number 1; number either clockwise or counterclockwise - lowest numbers

Nomenclature of Alkyl Halides Common name - Name the alkyl group first, followed by the name of the halogen expressed as an -ide name

Nomenclature of Alkyl Halides IUPAC name - The halogen is treated as a substituent

Nomenclature of Ethers Common name - Name(s) of alkyl group(s) listed first followed by the word “ether”

Nomenclature of Ethers IUPAC name - The smaller alkyl group is converted to an “alkoxy” name and used as a substituent

Nomenclature of Alcohols Common name - Name of the Alkyl group followed by the word “alcohol”

Nomenclature of Alcohols IUPAC name - The OH group is a site of reactivity (a functional group) Functional group is denoted by the suffix, “ol” methanol ethanol

IUPAC Nomenclature of Alcohols Parent Hydrocarbon is the longest continuous chain that contains the OH Number the chain in direction that gives functional group the lowest number If both a substituent and a functional group are present, the functional group gets the lower number

IUPAC Nomenclature of Alcohols If the functional group gets the same number when counted from both directions, use direction which gives the substituent the lower number If there is more than one substituent, cite substituents in alphabetical order

IUPAC Nomenclature of Alcohols System is summarized as [Substituent] [Parent Hydrocarbon] [Functional Group]

Nomenclature of Amines Common name - Name of the Alkyl group(s) (in alphabetical order) followed by the syllable “amine” The whole name is a single word methylamine methylpropylamine

Nomenclature of Amines IUPAC name - The NH2 group is a site of reactivity (a functional group) Functional group is denoted by the suffix, “amine” Final “e” of longest alkane group replaced by suffix “amine” 1-butanamine butan-1-amine

IUPAC Nomenclature of Amines Find the longest chain bonded to the nitrogen Final “e” is replaced with “amine” Number the carbon to which nitrogen is bonded Number any substituents on the alkyl chain Use italicized N- for each additional substituent(s) on the nitrogen

Properties of Alkyl Halides, Alcohols, Ethers, & Amines For alkanes, there are only induced dipole-induced dipole interactions (also known as van der Waals forces or London forces) van der Waals forces are a function of surface area

Induced Dipole-Induced Dipole Interactions

Hydrogen Bonding: Strong Dipole-Dipole Interactions

Dipole-dipole Interactions Particularly important for ethers vs. alkanes Ethers and alkyl halides have dipole moments, but their intermolecular attractions are not as strong as hydrogen bonds

Comparative Boiling Points

Solubility The more carbons that are present, the less soluble an organic compound is in water

Newman Projections A convenient way to describe conformation isomers is to look at the molecule along the axis of the bond of interest A Newman projection is a graphical representation of such a view

Conformations of Alkanes: Rotation About C-C Single Bonds

Chair Conformation of Cyclohexane

Drawing Cyclohexane in the Chair Conformation

Interconversion of Cyclohexane Conformations As a result of simultaneous rotation about all C-C bonds, a chair conformation of cyclohexane can interconvert to another chair conformation by a ring-flip In the process, equatorial bonds become axial and vice versa

Monosubstituted Cyclohexanes When there is one substituent on the cyclohexane ring, the two chair conformations are no longer equivalent

Conformations of 1,4-Disubstituted Cyclohexanes trans-1,4-dimethylcyclohexane two methyl groups on opposite sides of ring cis-1,4-dimethylcyclohexane two methyl groups on same side of ring

Conformations of 1,4-Disubstituted Cyclohexanes The cis isomer must have one substituent in an axial position and one in an equatorial position cis-1,4-dimethylcyclohexane ring-flip axial equatorial

Conformations of 1,4-Disubstituted Cyclohexanes The trans isomer has both substituents in either the equatorial or in the axial positions trans-1,4-dimethylcyclohexane ring-flip equatorial axial much more stable much less stable

Conformations of cis-1,3-Disubstituted Cyclohexanes A cis-1,3-disubstituted cyclohexane can exist in one of two conformations cis-1-tert-butyl-3-methylcyclohexane ring-flip much more stable much less stable

Conformations of trans-1,3-Disubstituted Cyclohexanes Both conformers of trans-1-tert-butyl-3-methylcyclohexane have one substituent in an axial position and one in an equatorial position