Orgo Unit 7.1 Discussion

Orgo Unit 7.1 Discussion - How do you think the pKa of the...

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How do you think the pKa of the following alcohol would compare to the pKa of 1- hexanol, why? (see attached image) The pKa of the hexa-1,3-dien-1-ol will be smaller than that of 1-hexanol. Why is this so? First, let’s consider what exactly the pKa value of a molecule tells us. The pKa value is defined as the – log Ka. So then, what does Ka tell us? Well, Ka = [A-][H3O+]/[HA], which is a measure of the strength of an acid in water. Compounds with a large Ka, have a smaller pKa, and are therefore more acidic. In this case, the Ka of the hexa-1,3-dien-1- ol is larger than the Ka of the 1-hexanol. Therefore, the pKa of the hexa-1,3-dien-1-ol is smaller than the pKa of the 1-hexanol. So then, what factors influence the Ka of a molecule, which we described above as the strength of an acid in water? We learned in Chapter 2 of the textbook that strong acids have weak conjugate bases. Alternatively, weak acids have strong conjugate bases. Therefore, the conjugate base of hexa-1,3-dien-1-ol is weaker than the conjugate base of
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This note was uploaded on 04/10/2011 for the course AAS 410.302.81 taught by Professor Thompson during the Spring '11 term at Johns Hopkins.

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Orgo Unit 7.1 Discussion - How do you think the pKa of the...

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