Growth in Known ompounds 70,000,000 60,000,000 50,000,000 54,675,250 63,175,733 50,000,000 40,000,000 29,988,150 30,000,000 20,000,000 10,000,000 0 50,000 144,000 300,000 11,669,292 18,000,000 1892 1910 1930 1992 1998 2006 2009 2010 2011 Year
There are many competing naming conventions:
Sometimes, the use of trivial names is particularly convenient:
IUPA Nomenclature alkane: alk an e a multiplicative prefix ( # of in parent chain) a functional group suffix a hybridization state suffix (sp 3, sp 2, sp)
Generating names of isomeric alkanes: 1. Find the longest contiguous hydrocarbon chain in the molecule. It becomes the PARENT, or 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 LOANTS. When there is a choice, assign substituents the lowest possible combination of locants determined by the first point of difference in locant. yphens 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. omplex substituents are encompassed by parentheses, or their common names are used.
Simple and complex alkyl substituents classification Primary (1E) Secondary (2E) R 3 3 R 3 R 3 3 3 Tertiary (3E)
IUPA and common names of constitutional isomers of the 3 and 4 alkyl substiutents substituent common name IUPA name 3 R n-propyl propyl 3 R 3 isopropyl 1-methylethyl or methylethyl 3 R n-butyl butyl 3 R 3 sec-butyl s-butyl 1-methylpropyl or methylpropyl 3 R isobutyl 2-methylpropyl 3 3 3 R 3 tert-butyl t-butyl 1,1-dimethylethyl or dimethylethyl
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
onformational analysis of butane viewed along the 2-3 sigma bond 3 3 3 3 3 3 3 3 3 3 3 3 0 60 120 180 240 300 E 0 60 120 180 240 300 360 1-2--3-4 dihedral angle, degrees clockwise
onformational analysis of 2,3-dimethylhexane viewed along the 3-4 sigma bond 3 3 3 3 3 3 180 120 60 0 300 240 E 0 60 120 180 240 300 360 2-3--4-5 dihedral angle, degrees clockwise
onformations of cycloalkanes Baeyer observed that the planar arrays of sp 3 -hybridized carbons which make up the constitutions of cylcoalkanes are generally distorted from the tetrahedral geometry: = 180(n-2), n where n = the number of in the cycloalkane parent ring. 60 90 108 120 129 So, the relative thermodynamic stability of cycloalkanes ( E / 2 ) should vary as a function of the Baeyer angle or ring strain.
Obviously, Baeyer s predictions were not accurate! Why? ycloalkanes 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. yclohexane appears to be able to adopt a conformation with no angle strain. an this conformation be determined?
All-staggered, chair conformations: yclohexane
2 2 2 2
chair chair twist-boat twist-boat boat half-chair half-chair 5.5 6.4 10.8
Alkylcyclohexanes: gauche vs. anti conformations and 1,3-diaxial interactions 2 2 2 2 3 3 with 3 axial, it is gauche to 2, but with 3 equatorial, it is anti to 2 another way to look at this gauche interaction: 1,3-diaxial interactions between axial substituents on the same side of the ring
ydrocarbons with more than 1 ring Spirocycles contain 1 common to 2 rings O spiro[4.5]decane β-vetivone
ydrocarbons with more than 1 ring Polycycles contain $2 common to $2 rings they have shared sides O O bicyclo[4.4.0] octane testosterone O O
bicyclo[3.2.1]octane camphor O
ydrocarbons with more than 1 ring atenanes share no a [2]catenane a trefoil knot
Twistane, 20 40 Olympiadane (1994) (a [5]catenane)