In my text book it states that a phosphate group is considered to be $\ce{-OPO3^{2-}}$. However, online it states that phosphate is $\ce{PO4^{3-}}$. Why do these contradict? Am i confusing phosphate the chemical with the phosphate group? Please see image for reference. enter image description here


Phosphate $\ce{PO4^3-}$ is an anion of the phosphoric acid $\ce{H3PO4}$. Term phosphate comes from a salt, for instance a sodium phosphate $\ce{Na3PO4}$. $\ce{Na+}$ are bound with a $\ce{PO4^3-}$ through ionic bonds. No electron sharing.

To annotate specific moieties of a molecule skeleton, a chemical group term is used. The phosphate has donated one pair of electrons on the oxygen to have a covalent bond with other molecule, for instance sugar in the image, and becomes a phosphate group in the molecule. Since the electron pair does not sit on the oxygen any more, but is shared with carbon, the phosphate charge is lowered to −2.

Phosphate group

  • $\begingroup$ Edl, please see below as I had to reply in the form of an answer to post an image in regards to your comment. $\endgroup$ – Atticus283blink Apr 24 '16 at 19:37
  • $\begingroup$ AMP is charged (-2) in physiological conditions (aqueous solution with pH~7). Both -OH groups are easily deprotonated (lost H+). The picture you have found shows a neutral molecule (which is right as well), and can be isolated in this state. $\endgroup$ – EdL Apr 26 '16 at 15:03
  • $\begingroup$ so the picture below (AMP with the OH- groups) are AMP outside of an aqueous solution where as the picture you originally gave in your answer is AMP deprotonated in water which is basically the phosphate anion? $\endgroup$ – Atticus283blink Apr 26 '16 at 15:12
  • $\begingroup$ Yes, that is right! $\endgroup$ – EdL Apr 27 '16 at 14:53

@ EDL, thank you. Im still confused on how the image above had a 2- charge. Im assuming the whole molecule is a formal charge of 0, correct? But if the 2 O atoms indicated in your drawing each have a 1- charge I would think the molecule would have a net charge of 2-? Also, why online does your image contradict the AMP I found. Please see below for image. Why are there H's where the phosphate group is and on your image the O's are alone with a "-" sign? Is what I have below the true AMP and what you were showing me was for the purpose of the functional group?

enter image description here

  • $\begingroup$ Please use the edit link on your question to add additional information. The Post Answer button should be used only for complete answers to the question. - From Review $\endgroup$ – Mithoron Apr 24 '16 at 20:23
  • $\begingroup$ Doesnt seem as efficient they need to add an option to add photos to a response hence why i added an answer $\endgroup$ – Atticus283blink Apr 24 '16 at 20:24
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    $\begingroup$ @Atticus283blink It's probably best to either integrate it into your question or host the image on imgur and link to it in the comment. $\endgroup$ – jonsca Apr 24 '16 at 21:58

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