There are various
types of arrows which are commonly used organic chemistry are discussed
here.
1. Forward arrow
The
forward arrow or it is also known as reaction arrow. This arrow is used for
indicating forward reaction. The reaction conditions such as reagents, solvent
and temperature is written on above or below the reaction arrow. Sometimes two are more reaction steps are
written on single arrow by giving numbers to each steps.
2. Dashed arrow
This arrow is
used when the reaction conditions are not discovered yet for particular
reaction. This arrow often used for showing future plan in multi step synthesis.
3. Equilibrium arrow
The equilibrium
arrow is used for representing reversible reaction. For example Reaction of
carbonic acid with water to give hydrogen carbonate is a reversible reaction.
It is also used for showing inter-convertible isomers of the molecules. For example conversion of Trans and Cis-azobenzene takes place in presence of light.
4. Non-equilibrium arrow
The
non-equilibrium arrow is used to indicate shifting of equilibrium towards
reactants or product. For example, benzoic acid reacts with aqueous hydrogen
carbonate to form benzoate and carbonic acid. In this reaction equilibrium
shift towards right side because carbonic acid is less
acidic than benzoic acid. Here the reaction is well defined by non-equilibrium
arrow.
The
non-equilibrium arrow is also used to show more prominent isomer from
inter-convertible isomers. For example, acetone has two inter-convertible
isomers in acidic medium. The keto-isomer is more prominent than enol-isomer.
The equation is described by non-equilibrium arrow.
5. Resonance arrow
The
resonance arrow is a double headed arrow. It is commonly used to represent
resonating structures of the molecule. For example, resonance structures of
benzene are shown by using resonance arrow. The structures I and II are
differing in position of double bonds.
6. Curved arrow (double headed)
The
double headed curved arrow is used to indicate relation between two groups. For
example, in one of the conformation of butane two methyl groups have “Gauche interaction”
this specify that methyl groups has dihedral angle of 60 °C. Here
the relation between two methyl groups is shown by using double headed curved
arrow.
7. Curved arrow (single headed)
The single headed curved arrow is used for representing movement of pair of electrons in various steps of reaction mechanism. For example, acetone reacts with hydroxide ion to form enolate. In the first step hydroxide ion donates a pair of electrons to one of the hydrogen to form cabanion. Here head of the curved arrow shows the movement of the electron pair from hydroxide ion to one of the hydrogen. In the second step the electron pair moves from carbon to oxygen. This is represented by two curved arrows.
8. Curved arrow (half headed)
The
half headed curved arrow depicts movement of single electron in organic
reactions. For example, chlorine molecule cleaves in to radicals in presence of
light. In this reaction cleavage of bond is shown by using two half headed
curved arrows.
9. Broken arrow (No reaction)
The broken arrow or no reaction arrow is useful to represent the reaction
when it is unsuccessful. For example, acetylene reacted with sodium hydroxide
to form anion but the reaction was unsuccessful. This is shown by using
broken arrow.
10.
Retrosynthesis
arrow
The
retrosynthesis arrow is a open arrow used for showing precursor of the
molecule. The retrosynthesis arrow is useful in multi step synthesis. For
example, benzoic acid can be synthesized by hydrolysis of benzonitrile. The
benzonitrile can be synthesized by substitution reaction from benzenediazonium
chloride. The backward synthesis is depicted by using retrosynthesis arrow.
11.
Clockwise
and Anti-Clockwise arrows
The
clockwise arrow used for indicating “R” configuration, whereas anti-clockwise
arrow is used for “S” configuration of the asymmetric carbon atom. If the direction
of priorities goes 1Ã 2Ã 3 clockwise then the
configuration is “R”. Similarly if the direction of priorities goes 1Ã 2Ã 3 anti-clockwise then it is
“S” configuration provided that H stands at back side of the plane of paper.
12.
Rotation
arrow
The rotation arrow is used
to depict rotation of the groups through single bond. The arrow helps to show
various conformers of the molecule.
13.
Rearrangement
arrow
As
the name suggest rearrangement arrow is used for representation of rearrangements in the molecule. For example, acetyl azide undergoes Curtius rearrangement reaction
to produce isocyanate. The reaction is shown by using rearrangement arrow.
To summarize this topic organic chemistry uses various types of arrow symbols to represent chemical equations.
|
Type of arrow |
Symbol |
Use |
|
Forward arrow |
 |
To depict forward
reaction. |
|
Dashed arrow |
 |
To show undiscovered
reaction condition. |
|
Equilibrium arrow |
 |
To show equilibrium in
the reaction. |
|
Non-equilibrium arrow |
 |
To depict more prominent
reactant or product. |
|
Resonance arrow |
 |
To represent resonance
structures. |
|
Curved arrow (double
headed) |
 |
To show relationship
between the groups. |
|
Curved arrow (single
headed) |
 |
To show movement of
electron pair. |
|
Curved arrow (half headed) |
 |
To show movement of
single electron. |
|
Broken arrow (No reaction) |
 |
To show unsuccessful
reactions. |
|
Retrosynthesis arrow |
 |
To show precursor of the
compound. |
|
Clockwise and Anti-Clockwise arrows |
 |
To show “R” or “S”
configuration. |
|
Rotation arrow |
 |
To show rotation of
single bond. |
|
Rearrangement arrow |
 |
To show rearrangement
reactions. |
That's all for this topic. If you have any questions please feel free to ask me. Also suggest me if any changes or additions are required. Thank you..!
No comments:
Post a Comment