# What is the systematic name of a “double benzene”?

Consider the molecule representation below. What is the systematic name of that molecule?

Could it possibly be 3,4-hex-2,6-anebenzene?

• The commonly used name is naphthalene, the systematic name is bicyclo[4.4.0]deca-1,3,5,7,9-pentaene – ron Dec 10 '14 at 17:42
• According to current IUPAC recommendations (2013), the preferred IUPAC name (PIN) is naphthalene. – Loong Jun 9 '15 at 19:58

Chemical Formula:

$\ce{C10H8}$

Common Name:

Napthalene (also accepted by IUPAC as per 1993 recommendations)

IUPAC Name: (refer numbering in figure)

Bicyclo[4.4.0]deca-1,3,5,7,9-pentaene or Bicyclo[4.4.0]deca-2,4,6,8,10-pentaene

For a general guideline:

• Start with one of the bridgehead carbons and number it 1.
• Proceed round the longest chain of carbons to the second bridgehead.
• Number the second bridgehead carbon and continue on round the next longest chain of carbons back towards the first bridgehead carbon.
• Pass over the first bridgehead carbon (it already has the number 1) and along the shortest chain of carbons to the second bridgehead carbon again.
• The generic name for compounds such as this is

bicyclo[x.y.z]alkane

• where x, y, and z are the numbers of intervening carbons on the three paths between the two bridgehead carbons cited in decreasing numerical order, and alk refers to the total number of carbons in the ring systems.

• Did you really mean to use equilibrium arrows instead of the resonance arrow? Please read the other answers and comments to see why the usage of "pentene" is incorrect. – ron Dec 10 '14 at 18:56
• Numbering of atoms in picture is wrong and everyone can edit Wikipedia (well everyone with access to internet...) – Mithoron Jun 9 '15 at 20:34

As @ron already said in his comment, the systematic name of the naphtalene is Bicyclo[4.4.0]deca-1,3,5,7,9-pentaene or Bicyclo[4.4.0]deca-2,4,6,8,10-pentaene since you can start the carbon numerotation from 2 chemically equivalent carbon.

You can find all the references here and here

• I thought you always use the lowest possible numbering system. It is not either or, or am I wrong? Is it really -pentene? You don't see -tetrene used, it is always tetraene. Google "pentaene" and see how many molecules with 5 double bonds are returned. I think -pentene is an error. – ron Dec 10 '14 at 18:05
• So you think it's pentaene ? – Babounet Dec 10 '14 at 18:12
• I do. Look at this analogous example: webbook.nist.gov/cgi/cbook.cgi?ID=C2443461&Mask=4 – ron Dec 10 '14 at 18:14
• Well, looks like you are right ;) I'll edit my answer then ! Thank you ron ! – Babounet Dec 10 '14 at 18:16