chemstruc: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/chemstruc - from package: chemical-structures

You may install the required package with command apt-get install {package}
Error in other languages:
chemstruc: bevel nie gevind nie
chemstruc: comandă negăsită
chemstruc: comando não encontrado
chemstruc: commande introuvable
chemstruc: command not found
chemstruc: käsku ei ole
chemstruc: không tìm thấy lệnh
chemstruc: komanda nerasta
chemstruc: Kommando nicht gefunden.
chemstruc: kommandot finns inte
chemstruc: komut yok
chemstruc: nie znaleziono polecenia
chemstruc: níor aimsíodh an t-ordú
chemstruc: no se encontró la orden
chemstruc: no s'ha trobat l'ordre
chemstruc: opdracht niet gevonden
chemstruc: parancs nem található
chemstruc: perintah tidak ditemukan
chemstruc: príkaz nenájdený
chemstruc: příkaz nenalezen
chemstruc: команда не найдена
chemstruc: командата не е открита
chemstruc: 命令找不到
chemstruc: コマンドが見つかりません