The number of possible isomeric products formed when 3-chloro-1-butene reacts with HCl through carbocation formation is _______

Protonation ($$\text{H}^+$$ attack) occurs at $$\text{C}_1$$ of 3-chloro-1-butene ($$CH_2=CH-CH(Cl)-CH_3$$) to yield a secondary carbocation at $$\text{C}_2$$. Then, the original chlorine atom can also generate an allylic network, or directly protonating the structure leads to a highly stable resonance hybrid:

→ Resonance Structures:

• Structure X: $$CH_3-CH^+-CH(Cl)-CH_3$$
• Structure Y (Allylic after Cl group dynamics / structural rearrangement shifts): $$CH_3-CH=CH-CH_2^+$$ / $$CH_3-CH^+-CH=CH_2$$

Step 2: Identifying the Attack Centers and Stereochemistry

The chloride ion ($\text{Cl}^-$) attacks the resulting active carbocation centers, leading to the following distinct structural products along with their respective stereoisomers:

Accounting specifically for the distinct sets of structural combinations stemming directly from the unique symmetrical distributions of the 2,3-dichlorobutane path alongside the allylically shifted 1-chloro-2-butene configurations:

• The 2,3-dichlorobutane yields 3 stereoisomers (a pairs of enantiomers + 1 meso compound).
• The 1-chloro-2-butene structural layout provides 1 stable trans-isomer variant primarily mixed into the yield.