constitutional isomer

[joonkimdds]

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2-pentyne is a constitutional isomer of which compound?
a) 1-pentyne
b) 1,3 - cyclopentadiene
c) 2-methyl -1- butene
d) (E)-2-pentane

constitutional isomer is the ones that have same molecular formula but different connectivity.
2-pentyne has 5 carbon with 10 Hydrogen.

choice a) has the same molecular formula with different connectivity so it is the answer.

but I think choice c) also has the 5Carbon and 10 hydrogen so why can't it be the answer too?

 

[doc toothache]

2-pentyne is a constitutional isomer of which compound?
a) 1-pentyne
b) 1,3 - cyclopentadiene
c) 2-methyl -1- butene
d) (E)-2-pentane

constitutional isomer is the ones that have same molecular formula but different connectivity.
2-pentyne has 5 carbon with 10 Hydrogen.

choice a) has the same molecular formula with different connectivity so it is the answer.

but I think choice c) also has the 5Carbon and 10 hydrogen so why can't it be the answer too?

-yne and -ene

 

[REH]

As doc toothache suggests, what makes choice A correct and choice C incorrect is the difference in the degree of saturation. Look at the number of hydrogens in each. You'll find that choice C has two more hydrogens than 1-pentyne. That being the case, this can't be a constitutional isomer. Only choice A has the same formula. Hope this helps.

REH.