dttom

Sorry for the late answering. If I- is expected to be more stable than Cl-, then I- should not be more nucleophilic than Cl-, as a more stable species should mount less attack (nucleophilic attack here). However, I- in fact is a stronger nucleophile than Cl-. One may argue that I- has a more diffused electron cloud that grants it the susceptibility, yet a counter-argument could be that it is because the electron cloud is more diffused so I- is more stable. Personally, I got some inspiration while studying the HSAB theory, I think it is because the carbon centre of an alkyl halide is a soft acid, and iodide is a softer base than chloride, so equlibrium constant for the reaction is greater for using iodide than using chloride.

I got it eventually, thanks for your detail explanation. Though the calculation of the event was settled, I still wonder why it should be like that, or why should the system rotate about its own centre of mass in the absence of a given axis of rotation (the pin in this case).

If there is a frame shift, certain manipulation should have transform the previous frame to the latter frame, what actually the manipulation should be? Because I nearly know nothing about frame shifting (though I could understand the relative example you quoted in the first reply), could you help me a little bit. What confuse me is, a reference frame is a set of chosen coordinate axis, but now I am describing an event that, when a rod is made to rotate about an axis other than the centre, the rod now just rotates about its centre axis when such a 'making pin' is removed.

I think it depends on cases, as it is not in case of sliding, but it is in case of rolling; without friction, no rolling could be done, and the frictional force acts through a torque to assist rolling.

If an energy source is required, once the fixed axis is removed, say there was a stick pin-through a point some distance from the centre, the rod-mass system still rotate about the original axis of rotation (the pin-hole)? But what observed in daily seems to reveal that an object tends to rotate about its own centre of mass regardless of how the initial rotation was.

I think the third option is most appropriate. I actually mean some other things else. I am trying to describe a phenomenon that any symmetric rotational object, without a fixed axis of rotation, would simply rotate around its centre of mass. That is, in the case discussing, the centre of the rod. I hope that makes it clear.

There are two masses connected by a light rod with length l, a vertical axis is at a distance x from one mass. Suddenly the axis is removed, and the system spontaneously has the axis shifted to the centre. L=mwx^2 + mw(l-x)^2 L'=2mw'(l/2)^2 = (mw'l^2)/2 L=L' (conservation of angular momentum) w'=w[(2x/l - 1)^2 +1] so w' must be greater than w. L = L', E = Lw/2 so the system energy increases, and I think this is illogical, how come a system can have its energy increases spontaneously (without any driving force)?

1&2) do you mean the person is on a piece of ice, and the piece of ice is on the pond? if so, you may use the momentum of the ice as your source of momentum... 3) your equation is largely correct, but 20 should be changed into 20mf, now you should be able to do that.

I suspect if the breast volume is proportional to mammary gland content, if so, individual with larger breast theoretically should have higher capacity of producing more milk (food)... Anyway, I just want to suggest two possible circumstances, and if you ask for evidence, I would say, no, these are just possible... cultural origin: An individual with supreme quality, if, for any reason (may or may not be evolutionary advantageous, but shouldn't be disadvantageous), appeal more to female of big breast size. Other individuals, following a trend of worshipness (a type of culture, and 'cultures' do exist in other primates), this preference could serve as an eliminating agent towards small breasts. Evolutionary origin: Breast size if proportional to food capacity available to babies, offspring could have evolutionary advantage if the females got big breasts. If one askes why it was human who did the trend but not other primates, there could have many answers, like evolutionary accidents, human having been confronted with a circumstance that milk production becomes especially important and hence selected under natural selection most...

I am considering modified form of Michaelis-Menton equation specially concerning non-competitive inhibition. The picture attached described what I have done... But why must K3 equal K4, I know it is the experimental result, but is there any actual reason can account for this?

maybe you can buy HCl, very cheap and much stronger than vinegar.

It is a question arose while I was dealing with MO of sulfuric acid manually. I adopted the ligand orbital approach, that is, to interact the four oxygen 'ligand' first. I interact the four s- ligand orbitals of the four oxygen, and get four MO (don't know if the word MO is appropriate or not, as it has not yet been a molecule) that would form four sigma bonds with sulfur atom. I followed the coordinate of 'xy coordinate on this plane (so the axis out from the computer screen is the z axis)'. Then I interact the four pz orbitals to form one orbital (a), two orbitals and one orbital (a*) which is the anti-bonding orbital for (a). Besides there are 8 non-bonding orbitals (NBO) contributed only by other p orbitals of oxygens. Now, I would like to know, whether the energy of (a*) is above NBO with (a) and the other two bonding orbitals below, or it is some other ways? A second topic I would like to discuss is about the structure of nitrate. I drew the MO diagram for NO3- for my interest, and the graph is in: If following the diagram probably the Lewis structure drawn would be obtained. But I am curious to know if the two ligand orbitals in rectangle are correct or not. I was told that, when 3 orbitals interact, there should be a bonding, an anti-bonding, and a non-bonding orbital, actually I can't distinguish which are which amongst this three (as well as (a) to ©, I think (a) to (d) are all bonding, because each overlap maximumly with s (sigma), py (sigma), pz (sigma) and px (pi) respectively).) But I am really not sure about (e) and (f)...

But if s-orbital is just overlapping side by side, there should be constructive interference, because it is not s- and px orbital of the same atom overlapping, there should not be cancelled interference, I think...

Consider: HI + Cl- <--organic solvent--> (eqm) HCl + I- Probably the eqm bias to the right, following the principle of strong base gives a weak base upon neutralization, it seems to be right to claim I- is a weaker Lewis base than Cl-. But my professor said I- is indeed stronger, why is that? It may be related to the polarizability of I-, which is bigger and electric charge more delocalized, thus being more polarizable than Cl-. This makes it more reactive towards a haloalkane than Cl- does. While on the other hand, as electric charge on I- is more dispersed than in Cl-, I- is more stable than Cl-. So a more stable I- reacts more rapidly than a less stable Cl- towards a given haloalkane? It seems to be a bit paradoxical. Maybe that, polarizability favours basicity as does basicity inferred from the neutralization reaction given above. So how do we take a balance, or, better, determine in between which one is a stronger Lewis base? And if in this case the factor of polarizability takes over basicity inferred, how can we say I- is a stronger Lewis base than Cl- with the reaction, HI + Cl- <--organic solvent--> (eqm) HCl + I-, in hand?

Yes the question is about whether polysubunit is needed. But it focuses on regulation rather than inhibition. I think regulation is different from inhibition that regulator binds to T state but allosteric inhibitor binds to R state. (otherwise regulator would have a lower max. reaction velocity, but the max. velocity remains in fact)

A competitive inhibitor binds directly to the active site and an allosteric one binds to an allosteric site away from the active site, both of them bind the enzyme in R state. So is the binding to R state by these inhibitor but the binding to T state of those regulators what make a difference? And why single chain protein, assuming it does have an allosteric binding site and flipping between T and R states, not be effective in regulation by these regulators?

For your first quote, it is absolutely correct that, in a natural environment, unfavorable genes would definitely be wipped out, with exceptions like that gene gradually became not so unfavorable and later became favorable or neutral, but these exceptions are not considered here. In an artificial environment, it is also true that natural selection is always in work, but the targets of which it works on could be manipulated. My opinion should be put more clearly that, medical technologies, like prolonging the life of some patients with genetic diseases, that without the technoloy such patients probably could not live to reproductive age, would alter the targets of which natural selection works on. In my example in the previous sentence, the gene for the genetic disease is now not so visible to natural selection, instead, it is the money, or ability to afford now visible to natural selection. Let's take an example, again the genetic disease in the first paragraph. Now there is 1% population affected, and 20% of population can afford the treatment. For 1st generation, there remains 0.2% affacted population; for nth generation, there remains 0.2^n% affected; eventually the disease tends to be wipped out. This is the case of having medical technology available. Now consider no such treatment, as there is no such treatment, eveyone who got affected could not live up to reproductive age, all die, for 1st generation, the affected population quickly drops to zero. Here shows a delaying effect of medical technologies on the disappearance of inherit diseases. Now consider generalization of accessibility of the treatment, the percentage of population that can afford now raises to 50%, the nth generation of affected population raises to 0.5^n%. There shows a longer delaying effect used by wider accessibility to medical technologies, and what is important is, this is the trend nowadays. For what I say 'not visible to natural selection' arise when the accessibility to the treatment goes to 100%, the affected population remains 1% or above, due to additional mutation. One could argue such hundred percent accessibility is not realistic, but at least there should exist an equilibrium that, the accessibility rises to a level that cancel out the effect of additional mutation leading to the disease. For your second quote, I could not say much, this of course should be controversial, and here I just like to speak out my view, and for the controversy and discussion continue. For your third quote, it would be settled if you agree first paragraph. And I think maybe this is due to our different interpretation in medical technologies? I think medical technologies target at body, instead of environment.

I was told that for an allosteric enzyme regulation to work, the enzyme in account should contain at least 2 subunits, but I can't understand why this is necessary. I think enzyme regulation is different from competitive inhibition as the former just stabilize the T state shifting the equilibrium but not directly competing for active site as in the latter case. And I think enzyme regulation is also different from non-competitive inhibition as non-competitive inhibition directly bind and inhibit the R state while the former just stabilize the T state, so it is in an equilibrium, an increase in substrate concentration could shift back the equilibrium. But this is not the case in non-competitive inhibition as the inhibitor also binds with the enzyme-substrate complex, a certain amount of active ingredient are definitely inactivated. I don't know these two understandings are correct or not. When I try to explain it by that, 'the enzyme must have at least 2 subunits as the binding of regulator would not directly affect the polypeptide chain containing the active site', this explanation should fail as I can't see any reason that a regulator binding to an allosteric site of an enzyme with single chain only when the enzyme is in T state could make any difference from an enzyme with 2 chains (subunits). I hope there are somebody to answer my question... even discuss is helpful... Thanks.

maybe... isopropyl alcohol --c.sulfuric acid--> propylene --HBr--peroxide--> 1-bromopropane--hydroxide--> 1-propanol

In the lecture I have just attended the professor talked about molecular orbital (MO) theory. He said a bond orbital, even for an individual orbital contribute so little that the contribution tends to none, should have an energy lower than all the contributing constituent orbitals. I have been thinking about this statement, and got some confusion in the following circumstance. If, now, we consider oxygen molecule, each oxygen has its 2s and three 2p considered. 1) The two 2s would form a bonding and an anti-bonding orbitals (1sigma and 2sigma*). 2) The two 2px would form a bonding and an anti-bonding orbitals (3sigma and 4sigma*). 3) The 2py and 2pz in each oxygen atom interact to form 4 MO in total, two bonding and two anti-bonding, all with pi nature (1pi, 2pi, 3pi* and 4pi*). Here we have 12e- in consideration (6 in each): 2 to 1sigma ---a 2 to 2sigma ---b (a and b cancel one another out) 2 to 3sigma 2 to 1pi ---c 2 to 2pi ---d 1 to 3pi* ---e 1 to 4pi* ---f (#due to half-cancelling capacity of 3pi* and 4pi*, c to f totally give just 1 pi bonding) The result would be 1 sigma bonding and 1 pi bonding. The above is what is usually interpreted. Now, actually 2s orbital of either oxygen should have, at least some, contribution to 3sigma (that formed between two 2px). But 3sigma certainly has an energy higher than the two 2s. Another thing is that I don't know if the statement in # is exactly the explanation or not, maybe there is other interpretations? So this is the case I want to discuss, please give some opinions. Thanks.

If assigning P for protein, L for ligand, then P + L <--> PL so isn't the Kd just (PL)/(P)(L) = (62.7-13.5)/(48.8)(13.5) = 74.7M-1

Probably the positive charge is better distributed if the carbon centre is more substituted by electron releasing effect of the substituent group, usually it would be alkyl group, so it would be the secondary which is more stable. But now the secondary carbon centre is bound to an alkyl group, with electron releasing stabilizing effect, but also to a electron withdrawing fluoro group which poses a destabilizing effect, so how could the balance be taken in this case?

Which one would be tertiary? I think one of them is primary and another is secondary...

I've just got question one solved... it is because, in organic chemistry, many elements involved are generally more electronegative than carbon so alkyl group is usually electron donating while the case change if the carbon is bonded with a more electropositive atom, like the case in carbanion. While I am still bothered by the second question. I have search for the bond length of C-F bond and of C-H bond. The former lengths about 1.34A and the latter about 1.1A. So C-F should be longer than C-H and be better participated by hyperconjugation effect, also is the C-C bond longer, while would this effect outweights the negative inductive effect due to strong electronegativity of F..., I'm not sure... Then the question could be put in another way... hyperconjugation between: ((1/3)vacant<->C-H bond)*3 --(A) ((1/3)vacant<->C-H)+((1/3)vacant<->C-F)+((1/3)vacant<->C-C)+(negative inductive effect from -F)+(positive inductive effect from -CH3) --(B) which one, (A) or (B), should be greater, if assuming stabilization as positive (or destabilization as negative)?

You are right in the product from B being more stable than product from A, either because it is more symmetric or through hyperconjugation and so according to Sayzeff's rule it is more stable. But if we consider the stability of intermediate it seems that intermediate A is more stable than intermediate B as A is a secondary carbonium ion better stabilized by hyperconjugation. So is there any paradox here?