Organik Kimyada Bileşikler

PROGRAM KODU
<?php
$OrgSnf=$_POST[OrgSnf];
echo "<form name='OrganikKimyasallar' action=$_SERVER[PHP_SELF] method='post'>
<table align='left'>
 <tr><td>Organik Sınıf</td>
   <td>:</td>
   <td>
    <select name='OrgSnf' size='1'>
     <option value='Alkanlar'>Alkanlar</option>
     <option value='Alkenler'>Alkenler</option>
     <option value='Alkinler'>Alkinler</option>
     <option value='Alkoller'>Alkoller</option>
     <option value='Eterler'>Eterler</option>
     <option value='AlkilHalojenurler'>Alkil Halajenürler</option>
     <option value='KarboksilliAsitler'>Karboksilli Asitler</option>
     <option value='Esterler'>Esterler</option>
    </select>
   </td></tr>
</td></tr>
<tr><td colspan='3' align='right'><input type='submit' name='Özellikler' ></td></tr>
</table>";

echo "<table border='1' align='center'><tr><th>Sınıfı</th><th>Genel Formülleri</th><th>Özellikleri</th></tr>";
echo "<tr>
          <td align='center'>$OrgSnf</td>
          <td align='center'>";
switch ($OrgSnf)
        {

        case Alkanlar:
        echo "  C<sub>n</sub>H<sub>2n+2</sub>
          </td><td align='center'> --- </td>
        </tr>";
        break;

        case Alkenler:
        echo "C<sub>n</sub>H<sub>2n</sub>
          </td><td align='center'> --- </td>
        </tr>";
        break;

        case Alkinler:
        echo "C<sub>n</sub>H<sub>2n-2</sub>
          </td><td align='center'> --- </td>
        </tr>";
        break;

        case Alkoller:
        echo "R-OH
          </td><td align='center'> --- </td>
        </tr>";
        break;

        case Eterler:
        echo "R-O-R'
          </td><td align='center'> --- </td>
        </tr>";
        break;

        case AlkilHalojenurler:
        echo "R-X
          </td><td align='center'> --- </td>
        </tr>";
        break;

        case KarboksilliAsitler:
        echo "R-COOH
          </td><td align='center'> --- </td>
        </tr>";
        break;

        case Esterler:
        echo "RCOOR'
          </td><td align='center'> --- </td>
        </tr>";
        break;
        }
if (empty($OrgSnf))
        {
        echo " 
          </td><td align='center'>   </td>
        </tr>";
        }
echo "</table>";
?>