Upper C subscript 2 upper H subscript 4 plus upper H subscript 2 right arrow upper C subscript 2 upper H subscript 6. Upper H subscript 2 plus upper C subscript 2 upper H subscript 4 plus 2 upper H right arrow 2 upper H plus upper C subscript 2 upper H subscript 5 plus upper C subscript 2 upper H subscript 6. Upper C subscript 2 upper H subscript 4 plus upper C subscript 2 upper H subscript 5 plus upper H subscript 2 right arrow upper C subscript 2 upper H subscript 5 plus upper C subscript 2 upper H subscript 6.