The Cahn–Ingold–Prelog (CIP) sequence rules, named for organic chemists Robert Sidney Cahn, Christopher Kelk Ingold, and Vladimir Prelog — alternatively termed the CIP priority rules, system, or conventions — are a standard process used in organic chemistry to completely and unequivocally name a stereoisomer of a molecule. The purpose of the CIP system is to assign an R or S descriptor to each stereocenter and an E or Z descriptor to each double bond so that the configuration of the entire molecule can be specified uniquely by including the descriptors in its systematic name.

1. -Minhaj Sohail Shakil Patel 1

2.  The Cahn–Ingold–Prelog (CIP) sequence rules, named for organic chemists Robert
Sidney Cahn, Christopher Kelk Ingold, and Vladimir Prelog — alternatively
termed the CIP priority rules, system, or conventions — are a standard process
used in organic chemistry to completely and unequivocally name a stereoisomer of
a molecule
 The purpose of the CIP system is to assign an R or S descriptor to each
stereocenter and an E or Z descriptor to each double bond so that the
configuration of the entire molecule can be specified uniquely by including the
descriptors in its systematic name
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3.  According to a procedure proposed by R. S. Cahn (The Chemical Society, London), Sir
Christopher Ingold (University College, London), and V. Prelog (Eidgenossiche Technische
Hochschule, Zurich), two steps are involved.
Step 1: Following a set of sequence rules we assign a sequence of priority to the four atoms
or groups of atoms attached to the chiral center. In the case of CHClBrI, for example, the
four atoms attached to the chiral center are all different and priority depends simply on
atomic number, the atom of higher number having higher priority. Thus I, Br, Cl, H.
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4. Step 2: We visualize the molecule oriented so that the group of lowest priority is
directed away from us, and observe the arrangement of the remaining groups. If,
in proceeding from the group of highest priority to the group of second priority and
thence to the third, our eye travels in a clockwise direction, the configuration is
specified R (Latin: rectus, right); if counterclockwise, the configuration is specified
S (Latin: sinister, left).
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5. Sequence Rule 1: If the four atoms attached to the chiral center are all different,
priority depends on atomic number, with the atom of higher atomic number
getting higher priority. If two atoms are isotopes of the same element, the atom of
higher mass number has the higher priority.
 For example, in chloroiodomethanesulfonic acid the sequence is I, Cl, S, H and in
α-deuterioethyl bromide it is Br, Cl, D, H
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6. Sequence Rule 2: If the relative priority of two groups cannot be decided by Rule I,
it shall be determined by a similar comparison of the next atoms in the groups
(and so on, if necessary, working outward from the chiral center). That is to say, if
two atoms attached to the chiral center are the same, we compare the atoms
attached to each of these first atoms.
 For example, take sec-butyl chloride, in which two of the atoms attached to the
chiral center are themselves carbon. In CH3 the second atoms are H, H, H; in C2H5
they are C, H, H. Since carbon has a higher atomic number than H, C2H5 has the
higher priority. A complete sequence of priority for sec-butyl chloride is therefore
Cl, C2H5, CH3, H
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7.  In 3-chloro-2-methylpentane the C, C, H of isopropyl takes priority over the C, H,
H of ethyl, and the complete sequence of priority is Cl, isopropyl, ethyl, H.
 In 1,2-dichloro-3-methylbutane the Cl, H, H of CH2Cl takes priority over the C, C,
H of isopropyl. Chlorine has a higher atomic number than carbon, and the fact
that there are two C's and only one Cl does not matter. (One higher number is
worth more than two or three of a lower number.)
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8. Sequence Rule 3: Where there is a double or triple bond, both atoms are
considered to be duplicated or triplicated. Thus,
 For example, in glyceraldehyde the OH group has the highest priority of all, and
the O, O, H of CHO takes priority over the O, H, H of CH2OH. The complete
sequence is then OH, CHO, CH2OH, H.
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9.  The phenyl group, C6H5 is handled as though it had one of the Kekule structures:
 In l-amino-2-methyl-l-phenylpropane, for example, the C, C, C of phenyl takes
priority over the C, C, H of isopropyl, but not over N, which has a higher atomic
number. The entire sequence is then NH2 , C6H5 , C3H7 , H.
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10.  Example 1- Example 3-
 Example 2- Example 4-
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11.  Example 5- In this example the lowest priority group is on the horizontal plane.
So for these types of examples we need to redraw the structure.
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12.  Example 6- In this example, the lowest priority group is above the plane. So bring
the lowest priority group behind the plane
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13.  Example 7- Example 9-
 Example 8-
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14.  Example 10- Example 12-
 Example 11- Example 13-
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15.  Example 14- This is an example in which there are two chiral centers present
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16. 1. Morrison RT, Boyd RN. Organic Chemistry, Allyn and Bacon. Inc.: Boston, MA,
USA. 1987:150.
2. Kalsi PS. Stereochemistry conformation and mechanism. New Age International;
2008.
3. https://en.wikipedia.org/wiki/E-Z_notation
4. https://en.wikipedia.org/wiki/Cahn-Ingold-Prelog_priority_rules
5. http://sayadimranpoc.blogspot.com/2016/11/cahn-ingold-prelog-rules-cip-rules-
for.html
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17. THANK
YOU 17