Isomers of pentene help!?

Question

Name all the cycloalkanes with the molecular formula C5H10. Include cis-trans isomers as well as constitutional isomers.

I'm a bit confused by the whole question. Why do they say cycloalkanes when it is the formula for pentene...typo? Anyway i need help with the names of the isomers it has.

Thanks

Answer 1

3-methylbut-1-ene is an isomer of pentene.

~But,

In addition to:

*pent-1-ene

*pent-2-ene (both E & Z )

*3-methylbut-1-ene

*cyclopentane

Consider:

*2-methylbut-1-ene

*2-methylbut-2-ene

*ethylcyclopropane

*dimethylcyclopropane

*methylcyclobutane  

Answer 2

For this problem you have to arrange 5 C-Atoms to a cyclic structure.

Start with a ring of 5 C-atoms. The name of this compound is

(1.) cyclopentane

If the ring consist only out of 4 C-atoms, which is cyclobutane. The fifth C-atom forms a methyl-group (-CH3), which is connected to one of the ring atoms. Since there is only one way to add single alkyl group  to an alkane, there is only on 4-ring alkane with this formula. It is

(2.) methyl cyclobutane

Smallest possible ring contains 3 C-atoms (=cyclopropane). The remaining 2C-atoms could form an ethyl group or two methyl groups. For the same as reason as mentioned above there is is only one structure with an ethyl group:

(3.) ethyl cyclopropane

For the two methyl groups there are two arrangenments. Either they are are connected to the same ring atom (1,1) or the are connected to different (1,2). For the later case you cis-trans isomerism.

due to the ring structure. The ring is rigid, that means the atoms or functional groups connected to ring atoms cannot rotate about the ring bonds. So these atoms/groups ar fixed in a position above or below the ring. So the the two methyl groups can be on the same side of the ring (cis) or on opposite sides (trans). Hence the last three isomers are

(4.) 1,1 dimethyl cyclopropane

(5.) cis 1,2 dimethyl cyclopropane

(6.) trans 1,2, dimethyl cyclopropane

Answer 3

Draw  cycles  with 3 ,4 and 5 carbon atoms.Then add the radicals needed to complete the number of C and H in your formula.

e.i . C3H6 is cyclopropane replace 2 Hydrogen in it and add 2   - CH3

then you have one of the isomers with formula C5H10.

Be care full it talks about Cyclo Alkanes!There are no double bonds.

Practice.