orbitals - Triple Bond Character in Acyl Chlorides

I am told that because of the poor overlap between a chlorine atom and a carbon atom and chlorine's relatively high electronegativity, there is a strong partial positive character on the central carbon in an acyl chloride molecule.

This makes sense. I am then told that because of this high partial positive character created through the inductive effect of chlorine and oxygen and the poor overlap between chlorine and oxygen, the oxygen's lone pair(s) actually participate in a sort of resonance with the central carbon, thereby giving the C=O bond in an acyl chloride partial triple bond character.

Is this true? Also what exactly is this called? Backbonding?

Answer

The various resonance structures that one can draw for an acid chloride are shown below.

Structure IV, is the "triple bond" structure that you mentioned. The acylium ion ($\ce{R-C#O^{+}}$) is very stable, so structure IV does contribute to the overall description of an acid chloride. Note that the $\ce{C#O}$ bond in IV is not a real triple bond as the carbon remains $\ce{sp^2}$ hybridized, with the attendant 120 degree (non-linear) bond angles. I've also drawn a fifth resonance structure involving hypeconjugation. This is probably a reasonable structure as well since it places negative charge on oxygen and positive charge on the hydrogen. It also helps explain why hydrogens on the carbon alpha to a carbonyl have increased acidity.

Usually the term "backbonding" is used when electron density is transferred from one atom to another through the use of antibonding orbitals. See here for a better description. In resonance structure IV, the lone pair from oxygen is being shared with an empty carbon $\ce{sp^2}$ orbital, the one that had been used to bond to the chlorine. I've never heard that referred to as backbonding.

equilibrium - Gibbs free energy-minimum or zero?

A reaction proceeds towards the direction of lesser Gibbs free energy (at constant $T$ (temperature) and $P$ (pressure)). So, we could say that Gibbs free energy at equilibrium is minimum.

On the other hand, we have $$\Delta G=\Delta G^\circ + RT\ln Q$$, where $Q$ is the reaction quotient. At equilibrium, $Q=K_\text{eq}$, and we already know that $\Delta G^\circ =-RT\ln K_\text{eq}$.

Substituting, we get $\Delta G=0$ at equilibrium. But, we know that $G$ minimized itself—thus there was a change in $G$ and $\Delta G < 0$.

What am I missing here?

Answer

I think your question really arises from some confusion about what $\Delta G$ represents. In general, $\Delta X$ for a thermodynamic quantity $X$ is the change of $X$ along some process. You could make it clear by actually writing $\Delta G(\text{A}\rightarrow\text{B})$ where A and B are before and after states. (We'll note that, in the general case, $\Delta X$ depends on the path take from A to B, making this notation improper. If $X$ is a function of state, though, you're good to go.)

However, in the equation you quote:

$$\Delta G = \Delta G^0 + RT \ln Q$$

the $\Delta G$ is a free energy of reaction and should thus be denoted $\Delta_r G$, with the correct equation being:

$$\Delta_r G = \Delta_r G^0 + RT \ln Q$$

The free energy of reaction is defined as $\Delta_r G = G_{\text{products}} - G_{\text{reactants}}$.

---

Thus, this $\Delta_r G$ is not the variation of $G$ over the entire reaction, which would be the $\Delta G$ of the system between the start of the reaction and the equilibrium.

---

PS: I think this link is the online resource I found with the clearer use and explanation of notations. Notations are important in thermodynamics!

thermodynamics - Validity of Trouton's Rule

I would like to know under what circumstances is Trouton's rule obeyed by liquids and why certain systems i.e. substances may deviate from Trouton's rule.

By the way I know what Trouton's rule is and I have a vague idea that sometimes Trouton's rule is not obeyed due to the presence of hydrogen bonding in liquids such as water but I would like to know more about other reasons why certain situations the rule is invalid.

halacha theory - How studying Torah without Machlokot is possible?

The idea of Machloket-less study and transmission of the Oral Torah is very basic in Judaism.

I spot two approaches:

1. 
   

   That of Sanhedrin 68b - there were Machlokot and different approaches and schools, but they were all settled by the working Sanhedrin:

   
   

   
   

   "תניא, אמר רבי יוסי: מתחילה לא היו מרבין מחלוקת בישראל, אלא בית דין של שבעים ואחד יושבין בלשכת הגזית"

   
   
   

   "... Rabbi Yosei said: Initially, discord would not proliferate among Israel. Rather, the court of seventy-one judges would sit in the Chamber of Hewn Stone... "

   
   

   
   


2. 
   

   That there were no different approaches, just as Moses didn't have them: Rashi (Sotah 47a see also Temurah 16a):

   
   

   
   

   "עד ימיהן לא היה מחלוקת בחכמי ישראל כולן היו אומרים דברים כנתינתן למשה"

   
   

   
   

While the first sound reasonable and feasible, the second sounds improbable and illogical: besides simple reciting mantras, discussing just anything leads to discords as a result of:

• 
  

  Differences in perception of the surrounding world - for example, time of sunrise, colors of stains, animal species or estimations of physical states (illness etc)

  
  


• 
  

  Finding new interpretations of the text

  
  


• 
  

  Different hierarchy of values (what overrides what)

  
  
  

Moreover, we can clearly see that Moses himself perceived the obligating (him) Halochos differently than what G-d told him, as in Breaking the Luchos, adding a day before Matan Torah, hitting the Rock and more.

I'm looking for a more comprehensive explanation of the approach that for over a thousand years studying of the Torah was Machloket-less.

particle が - How do you avoid multiple が in a sentence

I would like to ask on how to avoid multiple occurrences of the particle ga in a sentence. For example:

詳細{しょうさい}のクエリは削除{さくじょ}フラグが0がありません。

What I meant in the sentence: The Detail query does not contain the condition of "delete-flag equals 0".

Right now I would work around this by using equals symbol or change the verb like fukumemasen.

詳細{しょうさい}のクエリは削除{さくじょ}フラグ＝0がありません。

or

詳細{しょうさい}のクエリは削除{さくじょ}フラグが0を含{ふく}めません。

Is the original sentence's grammar correct? If not, are my alternative sentences correct?

Answer

I'm a little confused because 0がありません means "there is no zero".

Perhaps "delete-flag equals zero" should be ゼロの削除{さくじょ}フラグ or ゼロと等{ひと}しい削除{さくじょ}フラグ

---

I'm going to interpret your sentence as :

The Detail query does not contain the condition of "delete-flag equals 0"

Nouns: Detail query, (the condition of) delete-flag equals 0 (Not really a noun phrase unless interpreted as a condition)

Verb: contain

Negatives: (negates existence of "condition of delete-flag equals 0")

The sentence should be of the forms:

[Detail Query]には[Condition of delete-flag equals zero]を[not contain]

詳細{しょうさい}のクエリには ゼロと等{ひと}しい削除{さくじょ}フラグの状態{じょうたい}を含{ふく}めない - Condition of delete-flag equals zero is not included in the detail query.

詳細{しょうさい}のクエリは ゼロと等{ひと}しい削除{さくじょ}フラグの状態{じょうたい}がない - Condition of delete-flag equals zero is not present with respect to the detail query.

Alternatively, I think you can use the ~という construct.　i.e ゼロと等{ひと}しい削除{さくじょ}フラグという. Using this will turn the sentence into ... does not contain "delete-flag equals zero" (instead of condition of ~)

inorganic chemistry - Why is sulfur hexafluoride more stable than selenium or tellurium hexafluoride?

I was just reading about p Block elements from two different books. Both books say that $\ce{SF6}$ is extremely stable in 16th group due to steric reasons but my question is why is it more stable than $\ce{SeF6}$ and $\ce{TeF6}$ when $\ce{S}$ is more electronegative and smaller than $\ce{Te}$ and $\ce{Se}$ and so it would bring the electrons in bonding with fluorine closer to the central atom i.e $\ce{S}$ and thus it would bring the electrons closer and there would be more repulsion between the electron pairs.

Maybe this can be explained by Fajans rules that due to such conditions $\ce{SF6}$ has more covalent character than others and thus is more stable. But if this is the reason, where does "steric" come in here?

Answer

$\ce{SF6}$ is extremely stable for purely steric reasons, because S is completely blocked by fluorine atoms from all directions, so the reactions starting with an attack on S that otherwise would readily occur (hydrolysis, etc.) never have the chance to occur. This has nothing to do with electronegativity. For another similar example, look at $\ce{CCl4}$.

Now, the word "stable" is commonly used in two different senses. A compound may be stable by itself, i.e. not prone to spontaneous decomposition; in that sense $\ce{SF6}$, $\ce{SeF6}$, and $\ce{TeF6}$ are all totally stable under normal conditions, so there is nothing to compare. On the other hand, we may consider "stability" as inability to react with common reagents, e.g. water. In that sense $\ce{SF6}$ is indeed far more "stable" than the analogs, and that for the steric reasons (see above).

As for the thermal stability, that's another story altogether, so I don't really know how it would turn out. I wouldn't be surprised if $\ce{TeF6}$ would indeed happen to be the most stable of them all.

hashkafah philosophy - From where/Why do you get more reward for doing a obligated mitzvah than a non obligated mitzvah?

Ive heard (not sure where)that you get more reward for doing a obligated mitzvah than a non obligated mitzvah. Where is this brought down, and whats the reason for this?

Answer

The source that someone obligated in a mitzvah receives more reward than someone not obligated is a statement of R. Chanina which appears several times in the Talmud. The first appearance is Kiddushin 31a.

וא"ר חנינא ומה מי שאינו מצווה ועושה כך מצווה ועושה עאכו"כ דאר"ח גדול מצווה ועושה ממי שאינו מצווה ועושה אמר רב יוסף מריש ה"א מאן דהוה אמר לי הלכה כר"י דאמר סומא פטור מן המצות עבידנא יומא טבא לרבנן דהא לא מיפקידנא והא עבידנא השתא דשמעיתא להא דא"ר חנינא גדול מצווה ועושה יותר ממי שאינו מצווה ועושה אדרבה מאן דאמר לי דאין הלכה כרבי יהודה עבידנא יומא טבא לרבנן

Now, R. Hanina observed thereon, If one who is not commanded [to honour his parents], yet does so, is thus [rewarded], how much more so one who is commanded and does so! For R. Hanina said: He who is commanded and fulfils [the command], is greater than he who fulfils it though not commanded. R. Joseph said: Originally, I thought, that if anyone would tell me that the halachah agrees with R. Judah, that a blind person is exempt from the precepts,I would make a banquet for the Rabbis, seeing that I am not obliged, yet fulfil them. Now, however, that I have heard R. Hanina's dictum that he who is commanded and fulfils [the command] is greater than he who fulfils it though not commanded; on the contrary, if anyone should tell me that the halachah does not agree with R. Judah, I would make a banquet for the Rabbis. (Soncino translation)

Tosafot on the spot explains that the reasoning behind this is that an obligated individual goes through more worry and anguish that he might mess it up, while the non-obligated individual has nothing to worry about because he is not even obligated. The extra worry/anguish gets him extra reward.

נראה דהיינו טעמא דמי שמצווה ועושה עדיף לפי שדואג ומצטער יותר פן יעבור ממי שאין מצווה שיש לו פת בסלו שאם ירצה יניח

Ritva, in his commentary there, first quotes "our rabbis" as explaining that Satan goes after one who is commanded and not one who is not commanded. Therefore, one who is commanded receives more reward in accordance with the extra effort that was required.

פירשו רבותינו ז"ל טעם הדבר שזה שטן מקטרגו כשהוא מצווה וזה אין שטן מקטרגו ולפום צערא אגרא

He than quotes "our great rabbi" (Ramban) as explaining that one who is obligated fulfills the decree of the King by doing a mitzvah whereas one who is not obligated does not fulfill a decree of the King; hence the former gets more reward.

ורבינו הגדול ז"ל פירש שהמצות אינן להנאת האל יתברך המצוה אלא לזכותינו ומי שהוא מצווה קיים גזירת המלך ולפיכך שכרו מרובה יותר מזה שלא קיים מצות המלך