organic chemistry - Is buckminsterfullerene aromatic?

According to Wikipedia,

The $\ce{C60}$ molecule is extremely stable,^[26] withstanding high temperatures and high pressures. The exposed surface of the structure can selectively react with other species while maintaining the spherical geometry.^[27] Atoms and small molecules can be trapped within the molecule without reacting.

Smaller fullerenes than $\ce{C60}$ have been distorted so heavily they're not stable, even though $\ce{M@C28}$ is stable where $\ce{M\,=\,Ti, Zr, U}$.

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Some of us have heard and learned about the "rules" of aromaticity: The molecule needs to be cyclic, conjugated, planar and obey Huckel's rule (i.e. the number of the electrons in $\pi$-system must be $4n+2$ where $n$ is an integer).

However, I'm now very skeptical to these so-called rules:

• The cyclic rule is violated due to a proposed expansion of aromaticity. (See what is Y-aromaticity?)


• The must-obey-Huckel rule is known to fail in polycyclic compounds. Coronene^{figure 1} and pyrene ^{figure 2} are good examples with 24 and 16 $\pi$ electrons, respectively.


• Again, Huckel fails in sydnone. The rule tells you that it's aromatic, while it's not.

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The planar rule is not a rule at all. We're talking about "2D" aromaticity when we're trying to figure out the $n$ in $4n+2$. The "3D" rule is as following:

In 2011, Jordi Poater and Miquel Solà, expended the rule to determine when a fullerene species would be aromatic. They found that if there were $2n^2+2n+1$ π-electrons, then the fullerene would display aromatic properties. - Wikipedia

This would mean $\ce{C60}$ is not aromatic, since there is no integer $n$ for which $2n^2+2n+1 = 60$.

On the other hand, $\ce{C60-}$ is ($n = 5$). But then this rule strikes me as peculiar because then no neutral or evenly-charged fullerene would be aromatic. Furthermore, outside the page for the rule, Wikipedia never explicitly states that fullerene is not aromatic, just that fullerene is not superaromatic. And any info on superaromaticity is unavailable or unhelpful to me; including the Wikipedia "article" on that topic.

So, is $\ce{C60}$ aromatic? Why, or why not?

Answer

Aromaticity is not binary, but rather there are degrees of aromaticity. The degree of aromaticity in benzene is large, whereas the spiro-aromaticity in [4.4]nonatetraene is relatively small. The aromaticity in naphthalene is not twice that of benzene.

Aromaticity has come to mean a stabilization resulting from p-orbital (although other orbitals can also be involved) overlap in a pi-type system. As the examples above indicate, the stabilization can be large or small.

Let's consider $\ce{C_{60}}$:

• Bond alternation is often taken as a sign of non-aromatic systems. In $\ce{C_{60}}$ there are different bond lengths, ~1.4 and 1.45 angstroms. However, this variation is on the same order as that found in polycyclic aromatic hydrocarbons, and less than that observed in linear polyenes.

Conclusion: aromatic, but less so than benzene.

• Magnetic properties are related to electron delocalization and are often used to assess aromaticity. Both experiment and calculations suggest the existence of ring currents (diamagnetic and paramagnetic) in $\ce{C_{60}}$.

Conclusion: Although analysis is complex, analysis is consistent with at least some degree of aromaticity.

• Reactivity - Substitution reactions are not possible as no hydrogens are present in $\ce{C_{60}}$. When an anion or radical is added to $\ce{C_{60}}$ the electron(s) are not delocalized over the entire fullerene structure. However, most addition reactions are reversible suggesting that there is some extra stability or aromaticity associated with $\ce{C_{60}}$.

Conclusion: Not as aromatic as benzene

• Resonance energy calculations have been performed and give conflicting results, although most suggest a small stabilization. Theoretical analysis of the following isodesmic reaction

$$\ce{C_{60} + 120 CH4 -> 30 C2H4 + 60 C2H6}$$

suggested that it only took half as much energy to break all of the bonds in $\ce{C60}$ compared to the same bond-breaking reaction with the appropriate number of benzenes.

Conclusion: Some aromatic stabilization, but significantly less than benzene.

This brief overview suggests that $\ce{C_{60}}$ does display properties that are consistent with some degree of aromatic stabilization, albeit less than that found with benzene.

organic chemistry - What are the chemical process responsible for the warping of wood?

Background:

According to this Wikipedia article:

Wood warping costs the wood industry in the U.S. millions of dollars per year. Straight wood boards that leave a cutting facility sometimes arrive at the store yard warped. This little-understood process is finally being looked at in a serious way. Although wood warping has been studied for years, the warping control model for manufacturing composite wood hasn't been updated for about 40 years.

Factors contributing to the warping of wood include plant species, temperature and temperature changes, humidity and humidity changes and wet-dry cycles.

Discussion:

I'm not interested in which species are more prone to warping, how to prevent warping by treatments, etc. Nor am I interested in the biological processes of living or freshly cut wood. I'm interested in the processes happening over time on a molecular level that lead to macro-scale warping of wood. Water, in particular, seems to play a major role in the warping of wood, implying that possibly the lignin and cellulose matrix of wood is disturbed by the formation of hydrogen bonds. But if this is the case, or whatever the case, why would the microscale effects not cancel out rather than causing macro scale warping in a particular direction? This may be more of a physical than a chemical question, however.

Question:

What are the chemical process responsible for the warping of processed (as opposed to living or freshly cut) wood?

Edit 1:
A link to an interesting and relevant video was given in a comment, in which several types of wood were placed in a chamber which was evacuated of air, then pressurized with ammonia gas. The video also gave a link to a patent for this process. The following is an excerpt from the patent:

The rigidity of wood is the result of crosslinking between adjacent cellulose chains by water molecules which hydrogen bond between sites on adjacent cellulose chains. Anhydrous ammonia is extremely reactive with water, and it is believed that anhydrous ammonia scavengers water from wood, breaking the crosslinking between cellulose chains, and permitting the cellulose chains to slide, which renders the wood very flexible so that it can readily be bent or twisted. When the ammonia volatilizes from the treated wood, water vapor reestablishes crosslinking and rigidity.

The reason for this edit is to suggest that the disruption of hydrogen bonding between adjacent cellulose chains, when the wood is dried then rehydrated, for example, may also play a role in "natural" warping. I'm going to look into this more and I hope it gives somebody else a clue to a good answer.

grammar - Come to ～: ～てくる vs. ～ようになる

Can someone please explain the fine nuances of these two? Things such as:

• Are there conditions/restrictions of when you can use one or the other?


• What are the "approximate" time periods that each covers?



• Anything else relevant...

Here's an example I saw on a particular website.

• 最近Xの機能を使ってきたみたい、ね！　→　What it actually said


• 最近Xの機能を使うようになったみたい、ね！　→　What I thought it should have said

Answer

It depends on the aspectuality (or more specifically, telicity) of the predicate.

• With telic predicates like 現れる, 染まる, the event described involves a change of state. There is a change within the event before and after this point. With such predicates, various forms have the meanings such as the following:

現れている (perfect)
現れてくる (gradually 現れる towards the point of view of the first person)
現れていく (gradually 現れる apart from the point of view of the first person)
* 現れるようになる (ungrammatical)

• With atelic predicates like 使う, 走る, 食べる, the event described does not involve a change of state, and is homogeneous throughout (unless there is a direct object indicating an endpoint such as このボンベを使う, 100メートルを走る, おにぎりを一つ食べる). With such predicates, various forms have the meanings such as the following:

使っている (progressive)
使ってくる (使う on the way or before coming)
使っていく (使う on the way or before going)
使うようになる (gradually/eventually come to 使う)

There is no fixed time period for 最近. It depends on the context.

names - What is the greatest number of pages (daf) you can go in the Babylonian Talmud without encountering Abayei or Rava?

What is the greatest number of pages (daf) you can go in the Babylonian Talmud without encountering Abayei or Rava? I've heard it was 3?

gentiles - Is it permitted for a Ben-Noach be an atheist?

Avoda zarah is one of the things prohibited by the Seven Noachide Laws. But what about atheism? I know that the 7 Laws are often taken to include a larger number of halachot from the Torah, so would the prohibition against avoda zarah expand to include kefira as well?

Answer

Rav Moshe Feinstein, in a t'shuva about allowing children to say a generic prayer in public school (Orach Chayim II #24), refers to the Ramba"m's statement in Mishne Torah that Adam Harishon was given 6 commandments, including belief in God. No'ach and his descendants later got one more, adding up to 7. They both conclude that not only the negative aspect of believing in God is necessary - i.e. not serving other deities - but also the positive affirmation of His creation and provenance over the world, when circumstances call for it. Rav Moshe also uses the inference from the words of Ramba"m explained in @Yishai's answer.

aqueous solution - Why is water "the universal" solvent?

This is an old question that our textbook tried to answer but worsened the situation.

Many things are soluble in water. So many, that studying solutions will always require studying aqueous ones. It is true that many non-polars like waxes are not very soluble in water, yet I have never run into a solvent as "good" as water.

But how were we answered when we asked that "why is water a good solvent"? They said since water is polar so the attraction between for example $\ce{O}$ and the positive ions is so much blah blah blah!

So either there are "great" solvents like water out there or there are other things about water that make it the master solvent that are beyond me.

• Is there a solvent as "versatile" as water?


• Can this kind of solvent be non-polar?



• If the answer to the questions above is no, what is special about water?

Answer

To directly address where the phrase comes from:

Water is called the "universal solvent" because it dissolves more substances than any other liquid. -USGS

What are ideal qualities of solvent?

The strength of a solvent can be attributed to the strength of its intermolecular forces like london forces, dipole-dipole forces, ion-induced dipole, and hydrogen bonding. These are forces of attraction and repulsion. Solvation occurs when a molecule is surrounded by the solvent, so when there are strong intermolecular forces, stronger solvation occurs.

The hydrogen bond

Water makes use of the hydrogen bond, a type of intermolecular force experienced when hydrogen is attracted to the electronegative atoms nitrogen, oxygen, or fluorine. Hydrogen bonding is the strongest intermolecular force.

Hydrophobia

Water is a great solvent for hydrophilic molecules but hydrophobic molecules are, by definition, not easily disturbed by water. This makes a clear exception to the "Universal Solvent" idea. I haven't read any literature claiming it to actually be the best solvent, but it does work well in many chemical situations.

divorce - Is there any current rav or authority that issues conditional gittin?

I understand that King David would ask his warriors to give a conditional get (divorcec) to their wives prior to leaving for war. This way, if the wives did not hear about their husbands after the war was over, the wives would not remain agunot (women who can't remarry because their husband disappeared without giving a get), as the get would take affect at a certain time.

Someone I know is a Jewish army chaplain who is frequently sent to dangerous areas such as Saudi Arabia, Afghanistan, Iraq and other similar places. Occasionally he is with the troops during battles. He is away from home for months, sometimes a year at a time. He has considered the idea of giving his wife a conditional get, knowing well, that if he appears home after the time in the get, it would mean that his wife is divorced or even married to someone else. He knows that risk. He is wondering if there is anyone who currently can facilitate authorizing a conditional get.

Answer

Given that this is not an every day scenario, I don't think you'll find many Batei Din who will as a matter of policy issue conditional gittin. Nonetheless, that doesn't mean they will never issue them.

Rabbi Howard Jachter has an excellent pair of articles here and here that surveys more contemporary approaches to handling cases such as these. In the article, he posits that a conventional get followed by remarrying afterward is preferable according to many than a conditional get under normal circumstances.

Occasionally, however, a situation arises where it is appropriate to use a conditional get of some sort or another. He concludes that one should consult a Beit Din to determine which of the options he highlights should be used in a given case.