"A qualified domestic relations order – QDRO – is the document that transfers a portion of your 401(k) to your ex in accordance with the terms of your divorce decree. As long as you use one, there are no tax repercussions and the Internal Revenue Service doesn't treat the transaction as a withdrawal. QDROs are complex documents, but the task of creating one should not fall to you – you'll probably have to hire an attorney or accountant to draft one. "
Source: http://finance.zacks.com/tax-consequences-401k-divorce-settlement-4122.html
There is no deduction for giving half to your x-spouse.