# Tag Info

19

In fact, both reagents you noted here have quite complex structure and are not nucleophiles at all: both are electrophiles, because metallic atom here has too little neighbors to draw electrons from. Let me explain, using Grignard reagent $\ce{EtMgCl}$ . In reality it has complex structure with $\ce{Mg}$ atom coordinated to alkyl fragment and two diethyl ...

17

The character of the bond is determined by the electronegativity of the atoms. Speaking of bonds as purely ionic or covalent is not always correct - usually it is more correct to say that a bond has ionic or covalent characteristics. So comparing the difference in electronegativities gives us the following: $$\begin{array}{cc}\hline \text{Difference in ... 15 I am not sure if Silane (\ce{SiH_4}) can really be considered. But there are silicides which silicon forms with strongly electropositive metals. In these compounds, silicon has a negative oxidation state. For magnesium silicide - \ce{Mg_2Si}, the oxidation state of silicon would be -4. 13 That diagram is misleading because it’s technically in reference to bis(hexamethylbenzene)ruthenium(0). This is a famous example by the late and great E.O. Fischer. This Ru(0) complex is 18e, three methyl resonances were observed for the bent ring at −10 °C. Crystallography later confirmed this. This structure is surprising to the new student, perhaps, ... 12 The "real" structure of ferrocene is an iron atom sandwiched between to flat, parallel, pentagonal C5H5 rings. The diagram above shows the atomic positions from a crystal structure but the bonds are merely a convenience and don't accurately summarise the way the bonding works though the picture does accurately summarise the atomic positions in the crystal ... 12 It seems like an idea of using magnesium anthracene systems for the \ce{MgH2} production persisted since 1980s [1] till late 2000s, when new more efficient method with better scalability for industrial use was established. One of the recent reviews in hydrogen-storage applications [2, p. 220] compares the older two-step process of \ce{MgH2} synthesis: ... 11 You are correct. Grignard reagents \ce{RMgX} (where \ce{R} stands for some hydrocarbon group and \ce{X} is a halogen, usually \ce{Cl}, \ce{Br}, or \ce{I}) react with carbon dioxide to produce carboxylic acids after acidic workup:$$\ce{RMgX ->[1)\ \ce{ CO2}][2)\ \ce{ H3O+}] RCO2H}\ce{RMgX + CO2 -> RCO2- MgX+}\ce{RCO2- + H3O+ -&...

10

The difference in electronegativity between copper (1.9) and magnesium (1.3) is the key difference. Since copper is more electronegative than magnesium its electronegativity is much closer to that of carbon (2.55). This results in carbon-copper bonds being less polarized and more covalent than carbon-magnesium bonds. The electrons in a carbon-copper ...

8

Organotin compounds are rather toxic. They are also persistent in the environment and have a long biological half-life. The problem is that trialkyltin byproducts from your reaction are difficult to separate from the product. In the lab, this is painful and (usually) involves multiple columns, but when you want to get a drug past the FDA into the clinic ...

8

How Did Wittig Come to Discover Lithium-Halogen-Exchange? Georg Wittig, discoverer of the Wittig reaction, was studying the effect of ring strain on the strength of two neighboring carbons; by adding enough strain he expected to coax C-C bonds into forming diradicals: Unfortunately tetraphenylbenzocyclobutane rearranges to triphenyldihydroanthrancene ...

8

Copper is used to avoid lithium-halogen exchange. Additional information on that reaction can be found in this discussion. Organolithiums will often, instead of acting as a nucleophile, form a new organolithium: $$\ce{RLi + R'X <=> RX + R'Li}$$ Using $\ce{Cu(I)}$ allows the formation of an organocuprate, which acts as a nucleophile, allowing alkylation ...

8

@Huy ngo says it all. A Grignard reageant will react first with just about any hydrogen that has even a modicum of proton donation capability, before "resorting" to the slower nucleophilic attack. To get a ketone (in most cases), remove the dissociable proton by using a nitrile instead. This forms an intermediate imine which is hydrolysed to a ketone after ...

8

The IUPAC Goldbook provides no 'official' definition of the term heteroatom,and as such you're somewhat free to use (and abuse) the term as you see fit. Since no IUPAC definition exists, it may be helpful for you to define what you plan on calling a heteroatom at the beginning of whatever you're writing, to inform the reader (common practice in scientific ...

7

The difference between THF and epoxides is perhapse bigger than you might think. Due to the three-membered-ring of an epoxide, a lot of energy is 'stored' in ring strain. This destabilizes the stucture and is a driving force for a Grignard reaction (or any substitution on an epoxide). The THF is a five-membered-ring, which is far more stable. This bond is ...

7

It was a great effort. However, in the proposed name bis[(μ-2,6-{[2,6-di(1-methylethyl)]diphenyl}phenyl-1κC1,2κC7)chromium](5 Cr—Cr) I can see several issues: In you point 12: Forcing the metal-metal bond multiplicty in the name is interesting, however I wouldn't go against the rules. See the example with the multiple (triple) Cr-Cr bond, in the ...

6

As a result of the -I effect of the trifluoromethyl group, triflate is a better nucleofuge than mesylate and tosylate. As compared to tosylate and nosylate, triflate is rather small. This might be an advantage in reactions at "crowded" centres. Triflates do not undergo side reactions, such as hydrogen abstraction reactions, etc. A triflate, once ...

6

Unfortunately, you don't give an indication of what you expect the chemical shift for the -Me to be, other than higher than is observed. However, you are correct in your assumption; the π back donation from the Mn centre to CO ligands does decrease the shielding, and therefore does increase the chemical shift, but this is a good case of how chemical ...

6

TL; DR: coordination number of carbon atom in methyllithium tetramer is indeed 7, arising from 6 intramolecular interactions, as you suggested, and an extra bond with the lithium atom of the next tetramer. The key point is that you need to look beyond the tetramer. I'm sorry to inform you that the image from Wikipedia of the standalone cubane $\ce{Li4(CH3)4}... 6 The text box you are quoting from (p 219) refers to this specific reaction. The compound in question possesses an α-hydroxyl group, which needs to be deprotonated too. Notice that three equivalents of organolithium are needed in this reaction: one to deprotonate the acid, one to deprotonate the hydroxyl group, and one to react with the lithium carboxylate.... 5 Reaction of a Grignard reagent with an ester is a standard method for producing tertiary alcohols where at least two of the substituents (the "$\small\ce{R_2}$" group attached to the Grignard) are the same. Judicious choice of the starting ester allows for the preparation of a tertiary alcohol where all 3 substituents are the same. Alternately, you could ... 5 I appreciate the suggestions but some digging found a few possibilities: As I mentioned in the question, there's the Cambridge Structural Database, which includes over 700,000 compounds (both organic and inorganic/organometallic). It's decidedly not free, but available at many universities. There is the "Teaching Subset" of 733 compounds from CCDC which ... 5 Coordinated benzene as a dienophile It would be logical to suggest that an η4-benzene ligand could behave as a dienophile. The reason why benzene is characteristically unreactive, both as a dienophile and as a diene, is because of its aromaticity; if aromaticity is lost, one would expect it to become more reactive. However, to the best of my knowledge (and ... 5 A Grignard reagent is an organomagnesium halide of the generic form$\ce{RMgX}$, where$\ce{R}$is a hydrocarbon group and$\ce{X}$is a halide, usually$\ce{Cl}$,$\ce{Br}$, or$\ce{I}$. These reagents are produced by the reaction of magnesium metal with the corresponding organic halide in a non-protic (but coordinating) solvent, like diethyl ether. For ... 5 Turned in this report and my professor commented with his thoughts $$\ce{Sn + 2RCl \rightarrow R2SnCl2 \rightarrow R2Sn }\text{ (white solid)} \ce{+ SnCl2 \rightarrow R3SnCl}$$ but I didn't get the question wrong. So unless if someone contributes another answer, I'll accept this as the answer. 5 TLDR: Mercury in its (+2) salts does not have lone pairs readily accessible for covalent bonding. However, its 5d electrons do affect its properties, resulting in a relatively high polarisability. The long story: Mercury is the last 5d element and has electron configuration$[\ce{Xe}] 4f^{14} 5d^{10} 6s^2$. The$6s$electrons are the outermost electrons ... 5 The chloride can be a bit slow to react, particularly if the aryl halide is hindered. You might need a small amount of iodine to get the reaction started. (Maybe you ran into this already?) Once you form the Grignard, they should be identical for most applications. Personally, I would just go with iodide because the chloride is probably a bit less reactive,... 5 There's no way to predict this. Mnemonics are just rules, and rules are just rules. There will be exceptions, and you won't know when you should apply them a priori. If you could, it would be part of the rule by definition. The Curtin-Hammett conditions apply when the rate of interconversion between intermediates is significantly faster than the rate of ... 5 @tox123: You have generated two radicals on the same carbon by a two-electron reductive α-elimination (1 --> 2). So far, so good. In other words, you have created a carbene (2). Carbenes can rearrange to alkenes, NOT alkynes. Think of the two orbitals on the carbenoid carbon as one bearing two-electrons (negative) and the other one vacant (positive) (3)... 5 Some parts of this answer probably border a bit on personal opinion, but I will at least try to justify having such an opinion. The first thing to do is to actually examine the heterocycle. What kind of ligand is it? This is a carbene. It donates two electrons via the lone pair on the carbon in plane with the ring. Notice that there is a smear of positive ... 4 I don't remember a direct palladation of arylboronic acids or their derivatives in any of the couplings. Typically,$\ce{Pd(0)}$inserts into the$\ce{C-Hal}$bond of arylhalides and is thus oxidized to$\ce{Pd(II)}$. Ouite often,$\ce{Hal}$is then displaced with$\ce{OR}$by the action of a base. Think in$\ce{KOt-Bu}\$ often used in the Kumada coupling. ...

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