Rule A-4. Bivalent and Multivalent Radicals

4.1 - Bivalent and trivalent radicals derived from univalent acyclic hydrocarbon radicals whose authorized names end in "-yl" by removal of one or two hydrogen atoms from the carbon atom with the free valences are named by adding "-idene" or "-idyne", respectively, to the name of the corresponding univalent radical. The carbon atom with the free valence is numbered as 1.
The name "methylene" is retained for the radical 

Examples to Rule A-4.1

Methylidyne
Ethylidene
Ethylidyne
Vinylidene
Isopropylidene

4.2 - The names of bivalent radicals derived from normal alkanes by removal of a hydrogen atom from each of the two terminal carbon atoms of the chain are ethylene, trimethylene, tetramethylene, etc.

Examples to Rule A-4.2

Pentamethylene
Hexamethylene

Names of the substituted bivalent radicals are derived in accordance with Rules A-2.2 and A-2.25.

Example to Rule A-4.2a

The following name is retained:

4.3 - Bivalent radicals similarly derived from unbranched alkenes, alkadienes, alkynes, etc., by removing a hydrogen atom from each of the terminal carbon atoms are named by replacing the endings "-ene", "-diene", "-yne", etc., of the hydrocarbon name by "-enylene", "-dienylene", "-ynylene", etc., the positions of the double and triple bonds being indicated where necessary.

Example to Rule A-4.3

The following name is retained:

Names of the substituted bivalent radicals are derived in accordance with Rule A-3.4.

Example to Rule A-4.3

4.4 - Trivalent, quadrivalent and higher-valent acyclic hydrocarbon radicals of two or more carbon atoms with the free valences at each end of a chain are named by adding to the hydrocarbon name the terminations "-yl" for a single free valence, "-ylidene" for a double, and "-ylidyne" for a triple free valence on the same atom (the final "e" in the name of the hydrocarbon is elided when followed by a suffix beginning with "-yl"). If different types are present in the same radical, they are cited and numbered in the order "-yl", "-ylidene", "-ylidyne".

Examples to Rule A-4.4

Butanediylidene
Butanediylidyne
1-Propanyl-3-ylidene
Propadienediylidene
2-Pentenediylidyne
1-Butanyliden-4-ylidyne

4.5 - Multivalent radicals containing three or more carbon atoms with free valences at each end of a chain and additional free valences at intermediate carbon atoms are named by adding the endings "-triyl", "-tetrayl", "-diylidene", "diyl-ylidene", etc., to the hydrocarbon name.

Examples to Rule A-4.5

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