roundtrip: 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/roundtrip - from package: openbabel

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

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