From: "Paul Heelis" Subject: New chemistry jobs vacancy site To

Subject: ORGLIST: RNA hydrolisis
May someone give me some informations about the correct method to hydrolized

the RNA by chemical (basic) system?

Thank You very much
Alessandra
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Date: Thu, 09 Mar 2000 01:10:39 PST

From: "Alessandra B"

Subject: None
Hi, may somebody give me any informations about the method to digest the RNA

by chemical (basic) hydrolisis?

ThankYou very much
Alessandra
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Date: Thu, 9 Mar 2000 09:17:24 -0800

From: "Jack Kellum"

Subject: ORGLIST: thioacetal cleavage

Upon consulting Greene's book on protective groups, I see that cyclic

thioacetals (formed from aldehyde + ethane dithiol) can be cleaved with

mercury (II) perchlorate. OTOH, acyclic thioacetals (formed from aldehyde +

ethanethiol) are shown to be cleaved with a mix of mercury (II) chloride and

mercury (II) oxide. Is it reasonable to assume that the acyclic

dithioacetal will cleave with mercury (II) perchlorate? Is it six of one

and half a dozen of the other with respect to the two sets of conditions

effecting essentially the same cleavage? The reason I ask is that I have on

hand ethanethiol and mercury (II) perchlorate, but no EDT or other mercury

salts. I would think that the important thing is that mercury (II) is

present, and less important is the counterion. Any thoughts? Yeah, yeah, I

can always try the reaction on small scale and see if it works but before I

start generating mercury waste I'd like some informed opinions first.

Also, has anyone ever cleaved an acyclic dithioacetal with NBS? What might

the advantages/disadvantages be with the use of this reagent besides

avoiding the highly toxic mercury or silver salts usually employed in these

conditions?

Thanks in advance for all relevant responses.
Jack
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Date: Thu, 9 Mar 2000 09:52:39 -0800

From: "Chapman, Robert D"

Subject: RE: ORGLIST: thioacetal cleavage
Kocienski ("Protecting Groups") writes: "...there is little distinction in

the ease of formation or hydrolytic stability of cyclic

S,S-acetals...compared with acyclic congeners." He also cites a review on

thioacetals for protection: Groebel, B.T.; Seebach, D. Synthesis 1977, 357.

Kocienski gives an example of an acyclic dithioacetal cleaved by AgNO3. Is

that better for you?

Robert D. Chapman, Ph.D.

Chemistry & Materials Division (Code 4T4200D)

Naval Air Warfare Center

China Lake, CA 93555 USA

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Date: Sat, 11 Mar 2000 14:24:06 +0300

From: "Sam"

Subject: ORGLIST: Simple questions
Hi...This is Sam from Lebanon.

This is my first time here, so...Excuse me for my verry bad english :-)

I have some simple questions, I hope someone will help me finding the =

answers :

* Why after cooling (after heating) a solution that contains an organic =

(or non organic) compound with a specific solvant, this compound is =

recrystallised ?
*How does it happen that the melting point of a compound is a why to =

find its purity ?

*Why does polar solvents dissolve polar molecules, while nonpolar =

solvents dissolve non polar molecules.

I am new to the internet, if anyone can help find informations about =

these stuff ?

I am looking for a mailing list similar to this one, but about mineral =

chemitry...

Where can i find values of Kps or Ka for different compounds.
Thank you all verry much
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Date: Sat, 11 Mar 2000 14:06:50 -0500 (EST)

From: Christopher Paul Borella

Subject: Re: ORGLIST: Simple questions
Well Sam, I may be wrong but it sounds like you are trying to get us to do

your chemistry homework for you. I would sugest checking your text book

as all of this information should be present in any basic intro to

chemistry book or maybe even a general science book. If we simply give

you the answers it won't help you at all.
-Chris Borella

Dept. of Chemistry

SUNY Stony Brook

Stony Brook NY, 11794

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Date: Sat, 11 Mar 2000 21:08:09 GMT

From: "Yuehui Zhou"

Subject: None
I don't think any basic chemical book has explained why crystallization

occurs. They just put it as a common knowledge.

I think the question deals with the entropy and the total energy of a

system. A mixture system is not a stable one, that means it tend to transfer

into a state with less energy. But that needs some energy to overcome the

certain energy barrier. Heating a solution gives this energy so that the

system can reorganize into the state with minimal energy....crystallization

occurs.
The terms I used here to describe the process may be not suitable, but well,

hope somebody can use more exact language to explain this.
The second question I don't understand.
The third question is actually similar to the first one. The interaction of

the molecules with same polarity is the strongest. That means the system

with such interactions tend to sink the energy to the minimal. If you don't

believe it, try to do multiplying three times among 2,2,3,3,4,4 and add

three productions together. The biggest result is the addition of

self-multiplying of three numbers. Any other combination will produce

smaller result. This makes the system the most stable one. And natural

process always goes to the direction that leads to the stable state.

Yuehui Zhou
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Date: Sat, 11 Mar 2000 23:12:15 +0100

From: Shu-Kun Lin

Organization: MDPI (http://www.mdpi.org)

Subject: Re: ORGLIST: Simple questions on crystallisation and dissolvation
Your first and the last questions (I reproduced at the the end)

are very much related, one is crystallization, the other is

its reverse process. These bothered me a lot too when I was

a student. Yuehui Zhou is right, you cannot find any of its

satisfactory theoretical explanation in any textbook. During recent 10 years I

spent almost all of my weekend time on this problem. "Successful"

theoreticians call it (crystallization) self organization. Their new

theories only messed it up and useless to me as an experimental

chemist. If you do not mind, you may find my explanation at the

http://www.mdpi.org/lin/similarity/similarity.htm website.

Simply put it, if you want to "mix" (e.g., dissolve) several

components , simply increase their similarity. If you want to

separate them (e.g., by recrystallization), decrease their

similarity.

To reply the second question: good crystals after recrystallization

(same or most similar components get together) gives sharp

MP and higher MP because better crystal is more stable.

--

Dr. Shu-Kun Lin

Molecular Diversity Preservation International (MDPI)

Saengergasse 25, CH-4054 Basel, Switzerland

Tel. [phone], Fax [phone]

E-mail: [e-mail]

http://www.mdpi.org/lin/

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Date: Mon, 13 Mar 2000 12:16:25 +0000

From: "Rzepa, Henry"