# Parahexyl

Parahexyl, also known as synhexyl, is a synthetic homologue of tetrahydrocannabinol (THC) which was invented in 1941 during attempts to elucidate the structure of Δ$^9$-THC, one of the active components of cannabis.
Parahexyl is similar in both structure and activity to THC, differing only in the position of one double bond and the lengthening of the 3-pentyl chain by one CH$_2$ group to n-hexyl. Parahexyl produces effects typical of other cannabinoid receptor agonists in animals. It has a somewhat higher oral bioavailability than THC itself but is otherwise very similar. Presumably, it acts as a CB$_1$ receptor agonist in the same way as THC, but as there has been no research published using parahexyl since the discovery of the CB$_1$ receptor, this has not been definitively confirmed.
Parahexyl was occasionally used as an anxiolytic in the mid-20th century, the dosage ranging from 5 mg to 90 mg.
Parahexyl was made illegal under UN convention in 1971 on the basis of its structural similarity and similar effects profile to THC. Parahexyl was placed into the most restrictive Schedule I as a compound with no medical use.

## Isomerism

At least three isomers of parahexyl have been studied and are known to be active as cannabinoids. Parahexyl itself (i.e. the Δ$^{6a(10a)}$ isomer) has not had any significant use in scientific research since it was banned internationally in the early 1980s; however, the Δ$^8$ and Δ$^9$ isomers are both known to be cannabinoid receptor agonists, and Δ$^8$-parahexyl has the code number JWH-124, while Δ$^9$-parahexyl has been isolated from Cannabis plant material and assigned the name tetrahydrocannabihexol (THCH).
7 double bond isomers of parahexyl and their 30 stereoisomers :
| Dibenzopyran numbering | Dibenzopyran numbering | Dibenzopyran numbering | Monoterpenoid numbering | Monoterpenoid numbering | Number of stereoisomers | Natural occurrence | Convention on Psychotropic Substances Schedule |
| Short name | Chiral centers | Full name | Short name | Chiral centers | Number of stereoisomers | Natural occurrence | Convention on Psychotropic Substances Schedule |
| Δ$^{6a(7)}$-parahexyl | 9 and 10a | 3-hexyl-8,9,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol | Δ$^4$-parahexyl | 1 and 3 | 4 | No | unscheduled |
| Δ$^7$-parahexyl | 6a, 9 and 10a | 3-hexyl-6a,9,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol | Δ$^5$-parahexyl | 1, 3 and 4 | 8 | No | unscheduled |
| Δ$^8$-parahexyl | 6a and 10a | 3-hexyl-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol | Δ$^6$-parahexyl | 3 and 4 | 4 | No | unscheduled |
| Δ$^{9,11}$-parahexyl | 6a and 10a | 3-hexyl-6a,7,8,9,10,10a-hexahydro-6,6-dimethyl-9-methylene-6H-dibenzo[b,d]pyran-1-ol | Δ$^{1(7)}$-parahexyl | 3 and 4 | 4 | No | unscheduled |
| Δ$^9$-parahexyl | 6a and 10a | 3-hexyl-6a,7,8,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol | Δ$^1$-parahexyl | 3 and 4 | 4 | No | unscheduled |
| Δ$^{10}$-parahexyl | 6a and 9 | 3-hexyl-6a,7,8,9-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol | Δ$^2$-parahexyl | 1 and 4 | 4 | No | unscheduled |
| Δ$^{6a(10a)}$-parahexyl | 9 | 3-hexyl-7,8,9,10-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran-1-ol | Δ$^3$-parahexyl | 1 | 2 | No | Schedule I |
Note that 6H-dibenzo[b,d]pyran-1-ol is the same as 6H-benzo[c]chromen-1-ol.