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Reference Guide

Permachart - Marketing Reference Guide: Locant, Parent Structure, Substituent

2 pages1065 viewsFall 2015

Department
Chemistry
Course Code
CHEM 22700
Professor
All
Chapter
Permachart

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Side Chains & Groups
IsomerismAliphatic Hydrocarbons
The Cahn-Ingold-Prelog Rules
ALKANES
Carbon Compounds
• Organic chemistry is the study of compounds containing carbon
atoms (except CO, CO2, and carbonates)
Special characteristics: Carbon is tetravalent (forms four bonds with other
carbon atoms and/or other atoms like H, N, O, P, S, halides) • Carbon can form
stable double and triple bonds with other atoms to form all kinds of chain-
like and ring-shaped molecules, making the number of potential organic
compounds almost infinite (Note: Molecular formulas are not used in organic
chemistry because even the simple formula can represent many structures)
Saturated compounds have only single bonds (may be acyclic or cyclic)
• Unsaturated compounds have at least one multiple (double or triple) bond
between two carbon atoms or a carbon and another type of atom (e.g.,
>C=C<, C=
N, >C=O) • Aromatic compounds are cyclic with 4n + 2
delocalized pelectrons • Heterocyclic compounds are cyclic compounds
with at least one atom in the ring other than carbon (usually O, N or S)
• This set of rules designates the configuration of stereocenter (Ror S) or
stereochemistry of an alkene (Eor Z) • Each substituent is assigned a
priority by applying the following rules:
Rule 1 Priorities are first assigned on the basis of atomic number;
the higher the atomic number of the atom bonded directly
to the stereocenter, the higher its priority
Rule 2 For isotopes, the one with highest atomic mass has
highest priority
Rule 3 If priority cannot be assigned by applying Rules 1 and 2 because
two atoms of the same atomic number are bonded to the
stereocenter, then compare atomic numbers of the second
atoms in each group; continue comparing atomic numbers
as necessary until a difference is found
Rule 4 Multiple bonds are assigned single-bond equivalents
Fluoro
Chloro
Bromo
Iodo
Hydroxy
Methoxy
Mercapto
Methylthio
Amino
Acetylamino
Nitro
Acetyl
Methyl
Ethyl
Propyl
Isopropyl
Butyl
Isobutyl
sec-Butyl
tert-Butyl
Neopentyl
Benzyl
Vinyl
Allyl
1-Propynyl
2-Propynyl
Acyclic Alkanes, CnH2n+2 (n = 1, 2, 3, etc.)
CHIRAL CENTER: R-S NOTATION
Chiral center, chiral carbon atom,asymmetric
carbon atom, stereocenter or, more recently,
stereogenic center describe a tetrahedral carbon
atom that bears four different substituents
• Not all molecules which have a stereogenic
center are chiral (e.g., meso compounds)
• The precise arrangement of substituents at
a chiral center is its absolute configuration
• Absolute configuration (Ror S) is assigned
such that: (i) All substituents are ranked in
order of decreasing precedence according
to the Cahn-Ingold-Prelog Rules; (ii) The
molecule is oriented so that the lowest-
ranked substituent points away from you;
(iii) If the order of decreasing precedence
of the three highest-ranked substituents appear
in a clockwise sense, then absolute configuration
is R; if the order is counterclockwise, then S
ALKYNES, CnH2n–2*
1,3-hexadien-5-yne
not 3,5-hexadien-1-yne
ALKENES, CnH2n*
CIS-TRANS OR E/Z ISOMERS
NEWMAN PROJECTIONS
• Conformational isomers
(conformers) are
different spatial
arrangements of
a molecule that are
generated by rotation
about single bonds
• Each conformation
represents the same
molecule (same name)
• Different confor mations
may have different
stability: (i) Angle strain (deformation of bond angles); (ii) Torsional strain
(eclipsing of bonds); (iii) van der Waals strain (two atoms are too close
to one another)
Newman projection: Sight down the carbon-carbon bond and represent
the front carbon by a point and the back carbon by a circle
Anti, gauche, and eclipsed refer to 180°, 60°, and 0°, respectively,
between two groups (i.e., –CH3)
Nomenclature: Select longest continuous carbon chain for
parent name; characterized by suffix -ane Number carbons
in chain from either end so that first substituent has lowest
locant number • Basis for naming many organic compounds
Branched Alkanes
• Alkanes do not have a functional group so the name of a
branched alkane has the same stem and suffix -ane as
that of a straight chain alkane
Nomenclature: Determine the parent chain (longest
continuous carbon chain; if more than one chain has the same
length, choose one with the most branches) Number the carbon atoms in
the parent chain • If branch point is the same number of carbon atoms from
each end, then begin numbering at the end nearer the second branch point
• If still the same, then go further down the chain till first point of difference
• If numbering from either end gives the same numbers, begin numbering from
the end giving lower number to the substituent that comes first in alphabet
Identify the substituents; name each substituent and precede this name
with its locant (if two or more substituents are bonded to the same carbon atom,
repeat the same locant for each substituent) Use numerical prefixes (di-, tri-,
etc.) to indicate two or more identical substituents in a molecule Write the
name as a single word with all substituents arranged alpha betically as prefixes
When deciding the alphabetical order, ignore numerical prefixes (e.g., di-, tri-)
or prefixes used in common names like sec- or tert- Note: The names
isopropyl and isobutyl are accepted by IUPAC and the prefix
iso- is included as a part of the word’s alphabetization
• Unsaturated hydrocarbons that contain one or more C=C double bonds
Note: The double bond is considered a functional group
Nomenclature: Ending -ane in parent alkane is changed to -ene • Select
longest continuous chain containing both carbon atoms of the double bond
Number the chain from the end closer to the double bond (regardless of
positions of substituents) Identify substituents Identify stereochemistry
(cis- or trans- for disubstituted alkenes; E or Zfor di-, tri-, or tetra-substituted
alkenes) Write the name as a single word: first stereochemistry indicator,
then substituents, then locant of double bond, then stem of parent chain,
and, finally, suffix -ene
• Unsaturated hydrocarbons that have one or more carbon-carbon triple bonds
Nomen.: Ending -ane in parent alkane is changed to -yne Select
longest continuous chain with both carbon atoms of triple bond Number
chain from end closer to triple bond (regardless of positions of substituents)
Identify substituents Write the name as a single word: first substituents,
then locant of triple bond, then stem of parent chain, and, finally, suffix -yne
Note: The triple bond is considered a functional group • There are no
stereoisomers about the triple bond
Naming Organic Compounds
• Names of organic compounds consist of three parts: Substituents + Parent Chain Prefix + Functional Group
KEY TERMS
SIMPLIFIED RULES FOR NAMING ORGANIC COMPOUNDS
Locate highest ranked functional group
• Functional group is normally identified
by a suffix added directly to end of parent
chain prefix
Determine parent chain Parent chain is
longest continuous carbon chain that contains
highest ranked functional group and most
branches • Parent chain name is a prefix
deter mined by number of carbons in chain
Number the carbon atoms in the parent
chain • If the branch point is the same
number of carbon atoms from each end,
then begin numbering at the end nearer
the second branch point
Identify the substituents • Name each
substituent and precede this name with the
number of the carbon atom on the parent
chain to which it is bonded • If two (or more)
substituents are attached to the same carbon
atom, then give them the same number • Two
or more identical substituents in a molecule
are indicated by the use of the numerical
prefixes di-, tri-, tetra-, penta-, hexa-,
hepta-, octa-,nona-, deca-, etc.
Identify stereochemistry of the molecule
• Use cis-, trans-, (R), (S), (E), (Z) where
appropriate (with their locants, if necessary)
Write name of compound as a single word
• Names and numbers of substituents are
prefixes, parent chain is the stem of the name,
and functional group is the suffix • Hyphens
are used to separate various prefixes; commas
are used to separate numbers • Substituents
are arranged alphabetically
Numerical prefixes (di-, tri-, etc.) are not taken
into account when alphabetizing substituents
4 - m e t h y l - 2 - h e x a n o l
The parent chain of an organic compound
is the longest continuous carbon chain with
the highest ranked functional group • If two
different carbon chains with the highest
priority group and same number of carbon
atoms are possible, then the one with the
most branches is the parent chain
Substituents are atoms or groups of atoms
that replace hydrogen atoms on parent chain
Branches (or branch points) are carbon
atoms to which substituents are attached
Locants (numerical locations) are numbers
identifying carbon atoms to which a substituent
is bonded • All carbon atoms in the parent
chain are numbered in the direction that gives
the lowest number (1) to the highest priority
group, (2) to the substituent at first point of
branching, and (3) at first point of difference
Functional groups are atoms (or groups
of atoms) and their associated bonds that
define the structure and chemical properties
of a particular family of compounds (e.g.,
halogens, carbon-carbon double and triple
bonds, –OH, –NH2, carbonyl group (>C=O),
carboxyl group (–COOH) • Compounds
containing the same functional group undergo
similar reactions characteristic of that group
Isomers are compounds that have the same
molecular formula but different structures
Constitutional (formerly structural) isomers
differ in the order the atoms are connected
(i.e., bonds must be broken in order to make
two isomers equivalent)
Stereoisomers are compounds with the
same connectivity of all atoms but differing
in spatial arrangements of those atoms
CH3CH2CHCH2CHCH3
CH3OH
665544332211
Locant: Identifies
position of methyl
group on parent
chain
Prefix: Name
of substituent
attached to
the parent
chain
Parent chain +
suffix: The suffix
-e in the parent
chain (i.e., hexane)
is replaced by
the suffix -ol
identifying an
alcohol
Locant: Identifies
position of functional
group on parent chain
Note: The following common names appear frequently in the literature and
are accepted under IUPAC rules (IUPAC name in brackets): n-propyl (propyl);
isopropyl (1-methylethyl); n-butyl (butyl); t-butyl (1,1-dimethylethyl);
neopentyl (2,2-dimethylpropyl)
* Generalized formula for monoalkenes and monoalkynes
• Carbon-carbon double bond consists of a sbond and a pbond
pbond prevents free rotation about the C=C, so stereoisomers are possible
• Disubstituted alkenes and cycloalkanes may exist as cis-trans isomers; the
isomer is designated cis if both substituents are on the same side of the carbon-
carbon double bond or ring, and is designated trans if both substituents are on
opposite sides of the double bond or ring
E-Z system of nomenclature describes the configuration about carbon-
carbon double bond (alkenes) • Each group on the two carbon atoms of the
double bond is assigned a priority according to the Cahn-Ingold-Prelog rules
and the priorities are compared • The isomer in which the groups of higher
priority on each carbon atom are on the same side of the double bond is
designated (Z) • If the two groups of higher priority are on opposite sides,
the isomer is (E) • The E-Z system is more universal and may be used for
di-, tri-, and tetra-substituted alkenes • It cannot be used for cycloalkanes
The cis-alkene can be also named (Z)-alkene; trans-alkene can be also
named (E)-alkene (but not always vice versa)
E/Z and cis-trans stereoisomerism is not possible when one of the
doubly bonded carbon atoms bears two identical substituents
There are over 10 million known organic
com pounds; thousands are synthesized weekly
Parent name: Name of the alkane corresponding
to the longest continuous chain of carbon atoms
Substitutive nomenclature: Treats an
organic compound as a substituted alkane
(e.g., 1-bromobutane, 2-nitropentane)
Generic name: Name not directly derived from
systematic nomenclature; invented on request
(for a fee) by U.S. Adopted Names Council
Trade name: Name by which different
companies call a given product; trade names
are different from generic names
Systematic name: Name derived by
following a set of rules developed by IUPAC
(the International Union of Pure and Applied
Chemistry) • IUPAC rules have been updated many
times since the first conference in Geneva (1892)
The goal of the IUPAC rules is to arrive at a one-
word, unambiguous name for each compound
• No two compounds can have same name, but
it is possible to have multiple IUPAC names for a
particular compound (especially for complicated
structures)
CH3CH2CH2CH3
CH2CH2
O
CH2CH2
CH2
CH2
CH3
CH2
CH
butane
(unbranched,
open-chain) oxirane
(heterocyclic)
cyclopropane
(unbranched, cyclic)
methylcyclopropane
(branched, cyclic)
C CH
(CH3)3C
CHCHC
CH3
CH2CH3
3,3-dimethyl-1-butyne
CHCCHCH CH2
HC
3-methyl-1-pentyne
CHCH2CHCCH3CH2CH3
CH2CH3
CH2CH3
H3C
CH3
CH3CH
3,6-diethyl-
2,5,6-trimethyloctane
CH3CH2CCH2CH3
CH3
CH3
3,3-dimethylpentane
RS
ZZ
C
W
XX
Y
C
W
Y
mirror
C
W
ZY
RS
C
W
YZ
If X is loweste
ranked group
If priorities of W, Y,
and Z are increasing in
sequence (W<Y<Z), then
compound on the left is R
and the one on right is S
CH3
CH3
H
HH
H
CH3
H
H
HH
H3C
CH3
H
CH3
HH
H
rotate 60°
CH3
H
H
HH
H3C
H3C
H
H
H
H
H3C
H3CH
CH3
H
HH
rotate 60°
rotate 60°rotate 60°
rotate 60°rotate 60°H3CCCH2CCH2CH3
butane:
anti
(most stable
conformation)
gauchepartially
eclipsed
partially eclipsed
totally eclipsed
(least stable conformation)
gauche
Name the following compound:
• Hydrocarbons with only single bonds • Names of alkanes have suffix -ane
methane
ethane
propane
butane
pentane
hexane
heptane
octane
nonane
decane
1
2
3
4
5
6
7
8
9
10
CH2
CH2
CH2
CH3CH
CH2
(CH3)2CHCH
CH(CH3)2
CH2
CHClCH2
ethene
(ethylene)
propene
(propylene)
3-methyl-1-butene
(E)-3-methyl-3-hexene
2-methylpropene
(isobutylene)
CHCCH2CH2
CH3
C
CH3CH2
CH2CH3
C
H
CH3
2-methyl-1,3-butadiene
(isoprene)
chloroethene
(vinyl chloride)
H
H3CCH
2CH3
H
CC
H
HCH
2CH3
H3C
CC
CH3
CH3
H
H
CC
CH3
CH2CH3
H
H3C
CC
cis-2-pentene
or (Z)-2-pentene
trans-2-pentene
or (E)-2-pentene
2-methylpropene
(no stereoisomers
possible)
(Z)-3-methyl-2-pentene
(no cis-trans
equivalent)
-oic acid
-al
-one
-ol
-amine
-thiol
oxo-
oxo-
hydroxy-
amino-
mercapto-
halo-, alkyl-, aryl-, nitro-
Functional Group Suffix* Prefix**
*If higher precedence **If lower precedence
Note: Numbering begins from the
right side; therefore, the –OH group
(the highest precedence in the
compound) gets the lower number
Functional
Group
Priorities
TM
permacharts
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Organic Chemistry Nomenclature
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