J. LS
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"Middle row anomaly" of the periodic table
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28 votes

This is due to the transition metal contraction. Bromine has the electron configuration $\ce{[Ar] 4s^{2} 3d^{10} 4p^{5}}. $The 3d orbital has no radial nodes and is therefore quite contracted (close ...

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What is the viscosity of menstruation blood?
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12 votes

It is difficult to give a typical value as the composition and hence the physical properties of menstrual blood varies over the course of a woman's period. This reference has a good discussion which ...

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Why do dianions (such as malonate) bind cations more strongly than anions?
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11 votes

This is known as the chelate effect. The main reason why you observe this is that cations in solution have an ordered solvent shell around them, especially in polar solvents where there will be ...

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Why are silicon analogs of alkenes or alkynes so difficult to make?
11 votes

Just to add to ron's answer with some information on the properties of the silicon analogues. Silicon "alkynes" These exotic compounds were first reported on in 2004 in this paper. Typically show ...

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Is a carbon-fluorine bond stronger than a carbon-chlorine bond?
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9 votes

For free radical reactions, the most important parameter in assessing bond strength is bond dissociation enthalpy (BDE). Typical values for $\ce {C-F}$ bonds are around $\mathrm {100\ kcal/mol}$, ...

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Why doesn't Boron form Diborane with water?
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7 votes

I assume the hypothetical reaction you are asking about is: $\ce{3H2O + 2B -> B2H6 + 3/2O2}$ under standard conditions. The standard enthalpy of formation of water is −285.8 kJ/mol, whereas ...

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Why is the boiling point of heavy water more than that of normal water?
6 votes

The hydrogen bonds in deuterium oxide are slightly stronger than those in water. This is due to a quantum mechanical effect; the bonding interaction has a lower zero point energy due to the greater ...

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What is the the full name of TAPD? Structure provided
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5 votes

TAPD = Tetraalkyl-​p-​phenylenediamine This is because you have a phenyl (benzenoid) ring, with two amino groups (diamine) opposite (para) to each other, and each of those amino groups has two alkyl ...

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How to buy 1g of enzyme that is sold in units/mg?
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5 votes

Sigma Aldrich defines their units as: One pyrogallol unit will form 1.0 mg purpurogallin from pyrogallol in 20 sec at pH 6.0 at 20 °C. Assuming you're doing a biological imaging experiment, these ...

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why do we consider CuO as a base?
5 votes

An additional way to consider it: $\ce{CuO}$ is defined as a base in the Lux-Flood theory because it is an oxide ion donor; it donates oxide to oxide acceptors (Lux-Flood acids) An example of a Lux-...

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Stability variation in heavy nuclei
5 votes

The principle that "heavier nuclei are more stable" is a very crude approximation. Theoretical explanations of nuclear stability are complex. While the transuranium elements become progressively more ...

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Color of pheomelanin?
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4 votes

Pheomelanin has a very broad absorption spectrum in the visible, with monotonically increasing absorption as the wavelength decreases until a maximum is reached at 300 nm. I think that this would ...

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Compounds that adopt the zincblende structure
4 votes

Generally when you get a preference between two structures due to directional bonding, the first order environment of the cation is different. In this case however both are tetrahedrally coordinated. ...

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Why isn't this a compound?
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4 votes

This structure is impossible as either the molecule is planar and then the C-C bonds on the outer ring are extremely long (and therefore weak), or you distort from the sp2 geometry (120 degree bond ...

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Reduction of amides
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4 votes

You don't need to add water to produce the amine, but it's the simplest way of destroying any remaining hydride reducing agent (to give aluminium hydroxide, lithium hydroxide and hydrogen). Presuming ...

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Does hydrogen bonding strength correspond to Brønsted basicity in a given medium?
4 votes

There are several methods which can be used to compare the Brønsted-Lowry (proton-transfer) basicity and the hydrogen bond basicity. One of the most common defines a parameter $ \beta_{2} = (log K_{...

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Why are the three most simple alcohols completely miscible?
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3 votes

This happens because the intermolecular forces between different low molecular weight alcohols are very similar; as you say, they are dominated by hydrogen bonding. You can consider mixing on a ...

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What is the dipole moment of the most stable conformer of 1,1,2,2-tetrafluoroethane?
3 votes

The dipole moment is 2.45 Debye. The molecule is dipolar as you have asymmetrical electron distribution around both the carbon atoms. Source: Complete Structure of Gauche 1,1,2,2-Tetrafluoroethane ...

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The nuclear Overhauser effect
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3 votes

Consider the simplest possible NOE experiment, with two dipole-coupled protons, the target I and nearby proton S. Before the experiment there are four populated spin states: $\alpha_{I}\alpha_{S}$, ...

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Why are alpha-carbonyl relatively less stable?
3 votes

The carbon atom of the carbonyl group has a partial positive charge due to electron withdrawal by the electronegative oxygen atom. An $S_{N}1$ mechanism would result in an intermediate with a positive ...

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Why is hydrogen bonding more significant than any other interaction between dipoles?
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3 votes

Hydrogen bonds often have a significant covalent component. This can be seen in many aspects of the hydrogen bond: it is directional, unlike Coulombic interactions, and the bond length is generally ...

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Do Grignard reagents react with amides?
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3 votes

Amides will react with three equivalents n-butyllithium to give nitriles via geminal lithium oxyimide intermediates (J. Org. Chem., 1967, 32 (11)). n-butyllithium is a strong enough base to ...

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Is there a pH range for "neutral" detergents?
3 votes

Neutral detergents are not neccesarily at pH 7, and I know of no legal restriction (at least in the EU) on labelling detergents as neutral based on pH. For example, this patent claims protection for a ...

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Calculation of CFSE
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2 votes

Calculation for the first part: $\bar\nu_\mathrm{max} = \pu{20300 cm^-1},$ so $\Delta = \pu{4.03E-19 J}$ per molecule or $\pu{242.7 kJ mol-1}.$ $\mathrm{CFSE} = \pu{97.1 kJ}.$ $$\mathrm{CFSE} = \pu{...

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What kind of math should I expect in first year chemistry?
2 votes

There is relatively little mathematics required for a typical first year chemistry course beyond what most will have studied at school. A solid understanding of algebra, trigonometry and ...

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Organic synthesis problems
2 votes

Janice G. Smith's textbook "Organic Chemistry", while unfortunately expensive, has a good interactive workbook online which is useful even without the companion text. You can find it here.

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How to predict if hydrogen atoms could be placed in the interstials of a lattice
1 votes

Your intuition is correct; $\ce{NbH_{x}}$ retains the bcc Nb lattice, with the hydrides in the tetrahedral interstital sites, up to x = 2, when the compound switches to a fcc Nb lattice (the Fluorite ...

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Is it possible to predict the lines in the atomic emission spectrum of Na?
1 votes

The origin of the Rydberg equation is the Bohr model's equation for the energy of a hydrogenic state: $E_\text{B} = -\dfrac{R_{H}hc}{n^2}$ This is accurate for other hydrogenic atoms, with only one ...

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What does CH4 form when dissolved in aqueous solution?
1 votes

I think you are confusing dissociation with dissolution. Bonds do not need to be broken in order to dissolve a substance. The reason so many covalent compounds do disassociate in water is that water ...

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Strong Base combined with Sp2 carbons in Nucleophilic Substitution and Beta-Elimination Reactions
1 votes

The strong base is capable of being a nucleophile in this sort of situation; deprotonating tert-butyl alcohol will increase its nucleophilicity. In an SN1 reaction the overall rate is only dependent ...

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