Growth in Known Compounds 70,000,000 63,175,733 60,000,000 - - PowerPoint PPT Presentation

50,000 144,000 300,000 11,669,292 18,000,000 29,988,150 50,000,000 54,675,250 63,175,733 10,000,000 20,000,000 30,000,000 40,000,000 50,000,000 60,000,000 70,000,000 1892 1910 1930 1992 1998 2006 2009 2010 2011 Year

Growth in Known Compounds

There are many competing naming conventions:

Sometimes, the use of trivial names is particularly convenient:

IUPAC Nomenclature

alkane: alk an e a multiplicative prefix ( # of C in parent chain) a functional group suffix a hybridization state suffix (sp3, sp2, sp)

Generating names of isomeric alkanes:

• 1. Find the longest contiguous hydrocarbon chain in the molecule. It becomes the PARENT,
• r root, name.
• 2. Identify any substituent group replacing hydrogens on the parent chain.
• 3. Name each substituent group by derivation from its parent name:

alkane - ane + yl = alkyl These alkyl groups will be used as prefixes to the parent name of the compound.

• 4. Locate all substituent group position on the parent chain by numbering the

parent chain. These numbers are called LOCANTS. When there is a choice, assign substituents the lowest possible combination of locants determined by the first point of difference in locant. Hyphens always separate locants from letters in substituent names. Substituents are listed alphabetically as prefixes to the parent name.

• 5. Identical substituents are grouped and a multiplicative prefix is used:

di, tri, tetra, penta, hexa, etc.

• 6. Complex substituents are encompassed by parentheses, or their common

names are used.

R C H H C H H C H H CH3 CH3 C C CH3 R H H H R C CH3 CH3 CH3

Simple and complex alkyl substituents classification Primary (1) Secondary (2) Tertiary (3)

IUPAC and common names of constitutional isomers of the C3 and C4 alkyl substiutents substituent common name IUPAC name n-propyl propyl isopropyl 1-methylethyl

• r

methylethyl n-butyl butyl sec-butyl s-butyl 1-methylpropyl

• r

methylpropyl isobutyl 2-methylpropyl tert-butyl t-butyl 1,1-dimethylethyl

• r

dimethylethyl

CH3 C C H R H H H R C CH3 CH3 H R C H H C H H C H H H3C CH3 C C CH3 R H H H CH3 C C H R H H3C H R C CH3 CH3 H3C

Some examples 4-(1-methylethyl)heptane 4-isopropylheptane 2,3-dimethyl-6-(2-methylpropyl)decane 6-isobutyl-2,3-dimethyldecane not 6-butyl-2,3,8-trimethylnonane not 5-isobutyl-2-isopropylnonane

H H CH3 H H CH3 H3C H H H H CH3 H3C H H H H CH3 H H3C H H H CH3 H CH3 H H H CH3 H H CH3 H H CH3 0 60 120 180 240 300 360 C1-C2--C3-C4 dihedral angle, degrees clockwise E

Conformational analysis of butane viewed along the C2-C3 sigma bond

60 120 180 240 300

H CH3 H H H3C H H H H3C H H H H3C H H H CH3 H H H H CH3 H H

0 60 120 180 240 300 360 C2-C3--C4-C5 dihedral angle, degrees clockwise E

Conformational analysis of 2,3-dimethylhexane viewed along the C3-C4 sigma bond

180 120 60 300 240

Conformations of cycloalkanes

• Baeyer observed that the planar arrays of sp3-hybridized carbons which make up the

constitutions of cylcoalkanes are generally distorted from the tetrahedral geometry: CCC = 180(n-2) ° , n where n = the number of C in the cycloalkane parent ring. CCC 60 ° 90 ° 108 ° 120 ° 129 °

• So, the relative thermodynamic stability of cycloalkanes (E / CH2) should vary as a

function of the Baeyer angle or ring strain.

Obviously, Baeyer’s predictions were not accurate! Why?

• Cycloalkanes are not necessarily flat: they may be able to make conformational

changes that can reduce ring strain.

• The thermodynamic stability of a molecule is a function of

angle strain + torsional strain + steric interactions

• These factors are not independent: changing one can increase or decrease the others
• Molecules will adjust their conformations so as to minimize strains and interactions.
• Cyclohexane appears to be able to adopt a conformation with no angle strain. Can this

conformation be determined?

Cyclohexane

All-staggered, chair conformations:

H H H H H H H H H H H H H H H H H H H H H H H H H H H H C H2 H H H C H2 H C H2 H H H H C H2 H H H H

H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H chair chair twist-boat twist-boat boat half-chair half-chair

5.5 6.4 10.8

HH H H H H H H H H H H CH2 CH3 H H H H H H H CH2 H H CH2 H CH3 H H H CH2 H H H H H H H H H

Alkylcyclohexanes: gauche vs. anti conformations and 1,3-diaxial interactions with CH3 axial, it is gauche to CH2, but with CH3 equatorial, it is anti to CH2 another way to look at this gauche interaction: 1,3-diaxial interactions between axial substituents on the same side of the ring

O

Hydrocarbons with more than 1 ring

• Spirocycles contain 1 C common to 2 rings

spiro[4.5]decane β-vetivone

O OH OH O

Hydrocarbons with more than 1 ring

• Polycycles contain 2 C common to 2 rings

they have “shared sides” bicyclo[4.4.0] octane testosterone

O

bicyclo[3.2.1]octane camphor

Hydrocarbons with more than 1 ring

• Catenanes share no C

a [2]catenane a trefoil knot

Twistane, C20H40 Olympiadane (1994) (a [5]catenane)