Basic question

[deleted647690]

Hi, I know this is a really basic question

"Which of the following changes to n-propanol would NOT result in a lower pKa than n-propanol?

A. Oxidizing carbon 1 by four electrons, resulting in a pi bond to oxygen instead of two sigma bonds to hydrogen

B. Replacing oxygen with a sulfur atom

C. Replacing the propyl group with a phenyl ring

D. Replacing the OH group with an amine group."


The answer was D. For B, they said that the larger atomic radius of Sulfur allows for easier loss of the proton, which means that it is more acidic.

Then, for D, they said that the nitrogen in the amine group is less electronegative than oxygen, and thus it will not draw electrons as readily.


I was confused by this, because if you are looking at it as acid vs. base, couldn't you say that, because Nitrogen is less electronegative, it holds protons more weakly and thus will give them up more easily? (Thus making it a stronger Bronsted Lowry acid)

But if you look at it as nucleophilic base vs. electrophilic acid, their explanation makes more sense.

Why do they explain choice B in terms of Bronsted Lowry acid/base but choice D in terms of Lewis acid/base (electrophilicity/nucleophilicity)

(IE, proton donation vs. electron acceptance)?

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[aldol16]

You should not look at acidity and basicity in terms of nucleophilicity and basicity. Although nucleophilicity often parallels basicity, it doesn't always have to. Remember that nucleophilicity is a kinetic phenomenon whereas acidity and basicity are thermodynamic properties. This means that all you look for in acidity/basicity is the position of the equilibrium between the acid and base forms of the compound. The main question is: what affects that equilibrium and in which direction is it pushed?

So let's look at B. There's only one thing to consider. How stabilized is the thiolate (conjugate base form) compared to the thiol? Sulfur is less electronegative than oxygen so based on that factor alone, one would expect thiols to be less acidic than alcohols because sulfur wants that negative charge less (and thus wants to stay protonated). However, the dominant factor is the additional electron shell around the nucleus in sulfur. This makes the sulfur atom quite large relative to the oxygen and so the negative charge is spread out more. This tends to stabilize the conjugate base and thus make thiols more acidic.

Now let's look at D. We consider the same two factors - electronegativity and atomic radius. Here, the difference in atomic radius is negligible since nitrogen and oxygen are in the same row in the periodic table. That means electronegativity differences must dominate. Nitrogen is less electronegative and therefore does not want to build up negative charge as much as oxygen. Therefore, it'll be less acidic. Moreover, you should recognize that you almost never see amines act as acids. This is because the conjugate base of an amine is a negatively-charged R-NH compound, which is highly unstable. You usually only see ammoniums acting as acids.

 

[Pediateix]

i don't get these questions

which of the following statents apply to an autosomal dominate inheritance
i. a person needs a single cop of th mutant gene to inherit the disease
ii. AD trais do not skip generations ---why is this also correct. my understanding is that an AD trait has genotypes AaAa--couldnt this skip a generation since in the fourth box, the genotype will be aa



and also this question.

the following ar characteristics of an unknown inehitince pattern:
i. there is a 25 risk of having a homozygous normal child
ii there is a 25 risk of having a homozygous affected child
ii. there is a 50% risk of having a heterozygous child

the answer is autosomal receive. but if 25% is normal and healthy, then sholdint the disease be autosomal dominant?







and sorry for the questions but they involve the same concept
if a mother and father have one mutant gene for a disease with an autosomal dominant inheritance, what is their risk of having an affected childd.
0
25
75
50

answer is 75, but i thought that the AA would not even live and don't you typically not include it?

 

[aldol16]

ii. AD trais do not skip generations ---why is this also correct. my understanding is that an AD trait has genotypes AaAa--couldnt this skip a generation since in the fourth box, the genotype will be aa

aa skipping a generation wouldn't be the autosomal dominant trait skipping a generation. It would be the autosomal recessive trait skipping a generation. An autosomal dominant trait never skips a generation because there is no way to mask the allele. If the offspring have the allele, they will get the disease - no such thing as an autosomal dominant carrier.

the following ar characteristics of an unknown inehitince pattern:
i. there is a 25 risk of having a homozygous normal child
ii there is a 25 risk of having a homozygous affected child
ii. there is a 50% risk of having a heterozygous child

the answer is autosomal receive. but if 25% is normal and healthy, then sholdint the disease be autosomal dominant?

Is there any information you're excluding? Are the heterozygous children affected? Do we know anything about the parents? If the parents are heterozygous, you would get 25% homozygous dominant, 50% heterozygous, and 25% homozygous recessive. If the disease is recessive, that means only the homozygous recessives would be affected and the rest would be healthy. If the disease is dominant, that means that only the homozygous recessives would be normal and the rest would be affected. As you can see, either case fits the information you've given.

if a mother and father have one mutant gene for a disease with an autosomal dominant inheritance, what is their risk of having an affected childd.
0
25
75
50

answer is 75, but i thought that the AA would not even live and don't you typically not include it?

Crossing Aa with itself gives you AA, 2 Aa, aa and since it's dominant, AA and Aa would be affected. A mutant allele doesn't need to kill the child - it doesn't even need to be deleterious at all. Mutant in genetics just means different from the wild-type. So perhaps fruit flies naturally have red eyes but a mutation results in them having white eyes. It's a mutation but it doesn't have to affect their chances of survival.

 

[Pediateix]

aa skipping a generation wouldn't be the autosomal dominant trait skipping a generation. It would be the autosomal recessive trait skipping a generation. An autosomal dominant trait never skips a generation because there is no way to mask the allele. If the offspring have the allele, they will get the disease - no such thing as an autosomal dominant carrier.



Is there any information you're excluding? Are the heterozygous children affected? Do we know anything about the parents? If the parents are heterozygous, you would get 25% homozygous dominant, 50% heterozygous, and 25% homozygous recessive. If the disease is recessive, that means only the homozygous recessives would be affected and the rest would be healthy. If the disease is dominant, that means that only the homozygous recessives would be normal and the rest would be affected. As you can see, either case fits the information you've given.



Crossing Aa with itself gives you AA, 2 Aa, aa and since it's dominant, AA and Aa would be affected. A mutant allele doesn't need to kill the child - it doesn't even need to be deleterious at all. Mutant in genetics just means different from the wild-type. So perhaps fruit flies naturally have red eyes but a mutation results in them having white eyes. It's a mutation but it doesn't have to affect their chances of survival.

thank you . and about the question you said about having missing info. yea i had the same train of thought as you too. maybe the question is just worded weirdly. or maybe its just the homozygous that are affected.