Why does the + sign move to O in the addition of alkene with water?

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Discussion Overview

The discussion revolves around the behavior of oxygen in the context of the addition of water to an alkene, particularly focusing on the formal charge of oxygen and the implications of electron deficiency in this reaction. The scope includes conceptual understanding and calculations related to formal charges in organic chemistry.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant questions why the carbon in the alkene, which is initially electron deficient, is no longer electron deficient after the addition of water, and why the positive charge moves to the oxygen atom.
  • Another participant emphasizes the importance of calculating the formal charge on oxygen, noting that H2O has two lone electron pairs.
  • A follow-up question is posed regarding whether the oxygen becomes electron deficient after donating a lone pair to the positively charged carbon.
  • Further inquiry is made into the conditions under which oxygen is considered electron deficient, including the number of valence electrons required for neutrality and the implications for positive or negative charges.
  • One participant expresses a preference for understanding the reasoning behind formal charge calculations rather than relying solely on memorization, highlighting the importance of tracking electrons in organic chemistry.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the electron deficiency of oxygen and the implications of formal charge calculations. No consensus is reached on the specific conditions affecting the charge distribution in this reaction.

Contextual Notes

Participants reference the calculation of formal charges and the behavior of electrons in the context of organic reactions, but there are unresolved assumptions regarding the definitions and implications of electron deficiency.

kelvin macks
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Homework Statement



my question is at part 2 , since c form ch3ch2 is electron deficient, but after OH2 added in , with lone pair electron on O, the c should be no longer electron deficient anymore. am i right? why the + sign is moved to O now?

Homework Equations





The Attempt at a Solution

 

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Please calculate the formal charge on oxygen. Remember that H2O has two lone electron pairs.
 
ChiralWaltz said:
Please calculate the formal charge on oxygen. Remember that H2O has two lone electron pairs.

do u mean now the O become electron deficient, since one lone pair of lectron is donated to C+, and now there's one lone pair left one the O atom?
 
Why is oxygen electron deficient at this point? How many valence electrons should it have to be neutral? How many to be positive? How many to be negative? Do all atoms have the same requirements for their valence shells?

Hint: this deals with the calculation of its Formal Charge…
 
kelvin macks said:
do u mean now the O become electron deficient, since one lone pair of lectron is donated to C+, and now there's one lone pair left one the O atom?

That is not what I said but it is another, less formal, way of looking at the same thing. Knowing how to calculate formal charges is good because books and people can make mistakes. Keeping track of your electrons is incredibly important in O Chem. Once you have seen an oxygen with three sigma bonds and a lone electron pair 100 times, you probably won't need to run the formal charge calculations because you know it is positive.

I prefer to know why rather than rely on memorizing though. The memorization is simply a byproduct.
 

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