Dynamic WHERE and ORDER BY Clauses in SQL Server

SELECT *
    FROM MyTable
WHERE
    Col1 LIKE 
      CASE Col2
        WHEN '1' THEN 'X'
        WHEN '2' then 'Y'
        ELSE 'Z'
      END               

CREATE PROCEDURE GetEmployees ( 
    @ColName varchar(100) 
  ) 
  AS
    SELECT Col1, Col2
    FROM Employees
    ORDER BY
      CASE 
        WHEN @ColName='X' THEN CONVERT(char(50), Col1) + CONVERT(char(50), Col2)
        WHEN @ColName='Y' THEN CONVERT(varchar(50), Col1)
        WHEN @ColName='Z' THEN Z
      END