chemtoolbg: command not found

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

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

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 CentOS possible default full paths are:

/usr/bin/chemtoolbg - from package: chemtool

You may install the required package with command yum install {package}

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