Are CAS numbers universal?How do you read a CAS number?

October 17, 2023

CAS Registry Numbers (often referred to as CAS RN® or CAS Numbers) are universally used to provide a unique, unmistakable identifier for chemical substances.

Are CAS numbers universal?

CAS numbers, or Chemical Abstracts Service Registry Numbers, are not universal in the sense that they are unique to each chemical compound, but they are widely recognized and used in the scientific community as a standardized way to identify and catalog chemical substances. While CAS numbers are a valuable tool for chemical identification and are widely used in scientific literature and databases, they are not the only system in use, and different industries and regions may have their own methods for identifying and tracking chemicals.

You can find the CAS numbers of different chemical substances on LOOKCHEM’s website. Here are CAS numbers for some commonly used chemicals:

Chemical Name	CAS number
Phosphoric acid--N~4~-(6-chloroquinolin-4-yl)-N~1~,N~1~-diethylpentane-1,4-diamine (1/1)	5450-12-4
2-Benzyl-4-(dimethylamino)butanoic acid	1613-23-6
[(1S,2R,7R,9R,11R,12S,15S,16S)-8,8-difluoro-2,16-dimethyl-15-pentacyclo[9.7.0.02,7.07,9.012,16]octadec-5-enyl] acetate	4590-44-7
Semaglutide	910463-68-2
Carbon monoxide;cyclopenta-1,3-diene;diiodocobalt	12012-77-0
2,3,3a,4,7,7a-Hexahydro-1h-4,7-methanoinden-5-yl phenyl ether	7143-54-6
4-Methylpyrido[1,2-a]quinolin-11-ium chloride	6772-90-3
Pyridine-2,4,6-tricarbaldehyde	6390-09-6
Phosphoric acid--N~4~-(8-chloroisoquinolin-1-yl)-N~1~,N~1~-diethylpentane-1,4-diamine (1/1)	5432-15-5

How do you read a CAS number?

A CAS number, or Chemical Abstracts Service Registry Number, is a unique identifier for a chemical substance. It typically consists of three parts: The first part of the number, starting from the left, has 2 to 7 digits; the second part has 2 digits. The final part consists of a single check digit.

Here's how to read a CAS number:

Digits: The initial string of digits typically represents the chemical substance, but it's not necessarily indicative of the compound's structure. For example, let's take the CAS number for 2-Chloro-3-cyanopyridine as an example: 6602-54-6, the digits "6602" do not directly convey information about the chemical composition of water. Instead, they are a unique identifier assigned by the Chemical Abstracts Service.

Hyphen: The hyphen separates the first part of the CAS number from the second part. It helps break down the CAS number into distinct sections.

Check Digit: The check digit at the end of the CAS number is used for error-checking purposes. It ensures that the CAS number has been transcribed or recorded correctly.