Nomenclature for Heterocyclic compounds

Heterocyclic compounds

These are organic compounds that are formed by removing carbon with other atoms like O, N, F, S, etc. in the ring.

The nomenclature given below is necessary for proton NMR prediction. Here are some steps of Hantzsch-Widman nomenclature.

Nomenclature for Heterocyclic compounds

Hantzsch-Widman nomenclature

The Hantzsch-Widman nomenclature depends upon the type (Z) of heteroatom; the size of the ring (n) and ring nature, means if it is saturated (single bond) or unsaturated (double or triple bond) containing ring.

•    Hantzsch-Widman nomenclature useful for monocyclic compounds containing heterocycles having three to-ten-membered rings.

•      Prefix use for naming hetero atoms are shown as under:

•                                          O             Oxa

•                                           N              Aza

•                                           S             Thia

•                                           P         Phospha

👉Naming system for saturated or unsaturated rings:
Table 1:

 

Ring size	Saturated	Unsaturated	Saturated (With Nitrogen)
3	-irane	-irine	-iridine
4	-etane	-ete	-etidine
5	-olane	-ole	-olidine
6	Inane	-ine
7	-epane	-epine
8	-ocane	-ocine
9	-onane	-onine

 

👉 The ring size is indicated by a suffix according to Table 2 below. Some of the syllables are derived from Latin numerals, namely ir from tri, et from tetra, ep from hepta, oc from octa, on from nona, ec from deca.

Table 2:

Ring size	Suffix	Ring size	Suffix
3	Ir	7	ep
4	Et	8	oc
5 6	ol in	9 10	On Ec

👉When Assign number to heteroatom of heterocyclic compound use priority order that is

            O>S>Se>N>P>C

                       

Priority Order

·       👉  When numbering give priority to saturated substituent 

                                                               

priority order

     👉  To substituents attach to the ring always assign the lower number.

                                                                          

Assign lower number

 👉    Use complete word “Hydro” if hydrogen atom is present in the ring.

                                                                   

Use complete word

 👉  If rings are fused than number it as shown,

Number to fused rings

👉  When rings have bonds between them, numbering starts from heteroatom 

Number to fused rings

Here for example, if you want to write proton NMR then you must follow the sequence, write simple proton numbering first then single ` then double `` and so on, like

¹H-NMR (400MHz, CDCl₃): ⸹ value (d, J = value, 4H, H-3 to H-6), value of sigma (d, J = value, 2H, H-3` & h-5`) ……

·     👉 If extra hydrogen is present then it is necessary to show its position in the name of the molecule, so we use prefixes in italic capital ‘1H’, ‘2H’, etc. 

 show the position of Hydrogen

     👉     If you want to write proton NMR for the molecule, number the molecule as given in the structure by following the rules mentioned above,  then just open the ChemDraw software, draw the structure, the select structure then go to the structure mentioned in the bar of ChemDraw, then click on predict ¹H-NMR shift, now note the sigma values then write as i.e.

Number the molecule as this

 ^{i.e., 1}H-NMR (400MHz, CDCl₃): ⸹ value (d, J = value, 4H, H-3 to H-6), value of sigma (d, J = value, 4H, H-2` to  H-5`),.... write as if all sigma values are same if not then write separately as below,

 ^{i.e., 1}H-NMR (400MHz, CDCl₃): ⸹ value (d, J = value, 1H, H-3), value of sigma (d, J = value, 1H, H-4),..... & so on

For J value you should open the website and note the J value, below is the website address.

https://www.nmrdb.org/

• Predict 1D ¹H NMR spectra

 Point to Remember:

This method does not give 100 percent accuracy because you just supposed all the sigma and J value data, Accurate data is only obtained through a direct proton NMR machine.

For complete information click on the link given below

How to find or Predict Proton NMR 

See More

How Melting point shows variation in the heterocyclic compounds