Why do we call now a substituent or a group in organic chemistry “R” instead of a radical?

Answer 1

The sixth edition of "Organic Chemistry" by Paula Bruice addresses this.

We decided to distinguish between them and call a group with an unpaired electron a "free radical". It used to be said that "R" groups were radicals, yes. It was also said that the -OH in ethanol (EtOH) was attached to an ethyl "radical".

Historically, we have moved away from using the term "free radical" and have instead come to refer to "R" as a group, or substituent, and "radical" as a group that has an unpaired electron.

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Answer 2

Sarah Angotti

The use of "R" to represent a substituent or a group in organic chemistry is a convention that simplifies chemical structures and equations. It stands for "radical" historically but is used to indicate any substituent without specifying its identity.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.