Question

The IUPAC name of the compound

• A. 1 - bromo - 1 - chloro - 4 - 4' bicyclobutane
• B. 4 - (4' - chlorocyclobutyl) - 1 - bromocyclobutar
• C. 3 - bromo - 3' - chloro - 1, 1' - bicylobutane
• D. 4 - (4' - bromocyclobutyl) - 1 - Chlorocyclobutar

Answer 1

Answer: (B)

4 - (4' - chlorocyclobutyl) - 1 - bromocyclobutane

Answer 2

The correct naming is achieved by choosing one cyclobutane as the parent and the other as a cyclobutyl substituent. Since both rings have one halogen, we choose the ring with the substituent whose name comes first alphabetically as parent. Here “bromo‐” precedes “chloro‐”, so we take bromocyclobutane as parent and attach the other ring as a cyclobutyl substituent. In the parent ring the bromine is at C1 and the point of attachment is at C4. In the attached ring the original substituent chlorine (at C1 in its own ring) becomes located at the 4′–position (since the attachment is made via the opposite carbon). Thus the correct IUPAC name is

$$\textbf{4-(4'-chlorocyclobutyl)-1-bromocyclobutane.}$$

Brief Explanation:

• Two cyclobutane rings connected by a single bond can be named by treating one as the parent and the other as a substituent.
• Alphabetical priority gives bromine (bromo–) a lower number in the parent ring.
• The connection occurs at C4 of the parent and at C4′ of the substituent, which moves the chlorine from position 1 to 4′.