# Tag Info

21

cis-1,2-Dimethylcyclohexane is achiral, not because there is a plane of symmetry, but because it consists of two enantiomeric conformations which interconvert rapidly via ring flipping at normal temperatures. This is exactly the same case as amine inversion. "Chiral nitrogens" such as that in $\ce{NHMeEt}$ do not lead to chirality or optical activity ...

11

Short answer, no. There is not a "twist-chair." To convince yourself, it probably helps to make a physical model with a chemistry model kit. If you try to twist the chair, you can't do it without significantly moving at least one atom, in which case, the conformation is basically a "skew" or "twist boat." Try it. The boat and chair conformations are indeed ...

10

It says fully: TRUE OR FALSE: Boat cyclohexane is a slightly higher energy conformer than chair cyclohexane because: (a).... (a sub question) T OR F (b).... (a sub question) T OR F (c)chair cyclohexane has more axial hydrogens. T OR F The answer to part (c) of that question is "False." It turns out that the chair and boat conformations of cyclohexane ...

9

By symmetry, the cyclohexane on the right requires each carbon atom to have a $\ce{C-C-C}$ angle of 120 degrees. From VSEPR theory, this is not optimal for tetrahedral carbon. A regular tetrahedron has angles between vertices of approximately 109.5 degrees and the equilibrium bond angles of a secondary carbon won't be too discrepant from this.

9

Scientists are human beings after all. Nobody gets a Nobel Prize for inventing a "formula". It is the idea that makes an impact and new ideas are respected. Scientists like normal human beings make honest mistakes, but try their best to be correct. The guy who got the Nobel Prize in polarography, Hervosky, in the 1950s made errors in other electrochemistry ...

8

I think your problem with this reaction lies in the easily confused term syn and cis. Both appear to mean that two functional groups are oriented in the same direction. On a cyclic molecule, syn and cis are the same. However, cis is a stereochemical descriptor and syn is a conformational descriptor. Simplifying this reaction to an acyclic case may help. ...

8

I'd like to add a few points definition wise from the IUPAC goldbook. (Because recently the original website seems to be broken I am using links via the internet archive.) meso A prefix to indicate the presence of a symmetry element of the second kind (see chirality) in a chemical species which is usually one of a set of diastereoisomers that also ...

8

Chemspider tells me that the name should be 1,1'-Bi(cyclohexylidene) http://www.chemspider.com/Chemical-Structure.121798.html?rid=e40cd595-d5e5-450e-bdb3-3e558a9da92d While PubChem mentions: Cyclohexylidenecyclohexane https://pubchem.ncbi.nlm.nih.gov/compound/Cyclohexylidenecyclohexane My guess was maybe it's "cyclohexylene cyclohexane" There's ...

8

Take the molecule on the left and ideally flip it by rotating 180 degrees along the vertical axis of the diagram. This inverts the cyclohexane without having to break or modify the molecule in any way

7

TL;DR: It is highly unlikely that there is a non-multicyclic derivative with a stable boat conformation. It needs a lot of convincing and quite bulky groups to destabilise the chair conformation and stable another conformation like the twist-boat. Conformations of cyclohexane There are quite a few imaginable conformations,[1] but for cyclohexane itself ...

6

This type of reaction falls into the category of Grob fragmentation [Wikipedia]. Conceptually, it is very similar to an E2 mechanism, where an anti-periplanar pair of electrons flows into the sigma anti-bonding orbital of a carbon-leaving group bond resulting in a new pi bond and cleavage of the carbon-leaving group bond. The primary difference between ...

6

Pointing out the stable conformations of cyclohexane was a major part of Barton's Nobel Prize. His original review is here (paywalled, but you can see the first page). The topic is discussed by Henry Rzepa on his blog starting with a little history: Like benzene, its fully saturated version cyclohexane represents an icon of organic chemistry. By 1890, ...

6

It's not exactly clear from your question what distances you consider, but I have taken snapshots of a methylcyclohexane with the methyl group in the equatorial and axial positions:       (equatorial)    (axial) The distance of the methyl $\ce{H}$ atoms to the nearest cyclohexane $\ce{H}$ atoms are displayed, and you'll see that indeed the axial position ...

6

If you want to be very precise (perhaps pedantic), then I would conclude that the question itself is a little dubious without additional clarification. Consider the IUPAC recommendation on Basic Terminology of Stereochemistry. It contains the following definition of axial with respect to ring conformations (emphasis mine): In the chair form of cyclohexane ...

6

A reasonable chemist would be on the lookout for two products, especially given that E2 elimination from 1-bromo-1-methylcyclohexane produces some methylenecyclohexane In the transition state for the E2 elimination the pi bond is already partially developed. This means that the relative thermodynamic stabilities of the products will play a role in ...

6

Sometimes, the intuitive rule of thumb that favours conformations with $\ce{OH}$ substituents in equatorial positions miserably fails. For 1, a cyclization product of geranyl acetate, one might assume that the favoured conformation in solution and in the crystal is 1eq. However, this is not the case! Both NMR spectroscopy and X-ray crystallography indicate ...

6

The lowest energy conformer for a cyclohexane ring with multiple substituents will be the one in which the largest group occupies an equatorial position. Steric parameters are tabulated in many organic chemistry textbooks, the most common of which is the A-value. The A-value represents the difference in energy (ΔG) between a group being axial/equatorial on ...

5

If the elimination occurs via an ${\mathrm{E_2}}$ mechanism, the other endocyclic double bond (i.e., the one between the two methyl bearing carbons) cannot be formed, as the $\ce{C_2}$ $\beta$-hydrogen will not be anti-periplanar to the $\ce{Br-}$ leaving group. That said, the other possible elimination product you've identified, with the exocyclic double ...

5

In my exam, my teacher asked me if the following is true: "The chair cyclohexane has more axial hydrogens" I did not have time to think, so I just put false. And apparently I was right. What's the complete question? The chair form has more axial hydrogens than what other form? If the test were referring to the other chair conformation, then you are right. ...

5

I'm having quite a fair bit of trouble comprehending the hybridization of cyclohexane. Atoms can be hybridized. Not entire molecules. Just atoms. I understand that this is a ringed structure with single C-C bonds, therefore all the carbons should have sp3 hybridization right? Yes, all the carbons in cyclohexane can be said to be sp3 hybridized. ...

5

So if you drew a wedge in position 1 and a dash in position 2, it would mean that they are on the same plane - either both axial or both equatorial - assuming that the ring was in a chair conformation. However, if the objective is to show the structural isomers very clearly, it may be better to use either the chair conformation sketch: ... or the Newman ...

5

While you are correct that B should be the most stable conformer of trimethylcylcohexane, the question asked which one best represents the one shown in the Haworth projection. Answer choice B has R stereochemistry on carbon B (see below), while carbon B has S stereochemistry in the original projection. As such, the initially drawn compound is different from ...

5

Assemblies of two identical rings linked by a single bond are described in the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) as follows: P-28.2 RING ASSEMBLIES OF TWO IDENTICAL CYCLIC SYSTEMS P-28.2.1 Ring assemblies with a single bond junction Assemblies of two identical cyclic ...

5

Cyclo comes from the Greek word 'kyklos' which means circle. The cyclohexane molecule is in the form of a circle therefore it can have the formula $\ce{C_nH_{2n}}$ and still be saturated.

5

@Waylander provided a correct written explanation for your question. I'll expand on his comments by considering the effect of temperature and provide diagrams. Using M+ = Sc+3 to save some space, the Lewis acid coordinates with the more basic of the two acetate oxygens in 1 to provide the reactive oxonium species 2. [The oxonium species is planar about the ...

4

In compund 2, both substituents can be placed in equatorial positions, whereas in 1 the $\ce{Cl}$ group is forced into an axial position since the bulky t-butyl group has to be placed equatorial. This makes compound 1 more unstable (higher energy), leading to a faster rate of formation of the carbocation.

4

If we get rid of the two methyl groups and just consider what the 3D conformation of the molecule is likely to be (I don't have a pen on me right now, but the model below was minimised using very low level molecular mechanics). What we can hopefully see is that there is very much a convex face and a concave face of this molecule. In the absence of all ...

4

You can't have both in a chair conformation! If the methyl groups in 1,4-dimethylcyclohexane adopt a bis-axial orientation, they are trans and they stay trans after ring flip: If your 1,4-dimethylcyclohexane is cis-substituted the orientation of the methyl groups is axial and equatorial, respectively:

4

There are not many reputable sources on the matter (as I could find) since it seems that cycloheptane isn't the most popular chemical around (poor guy) but I will present you with the best explanation/argument/insight into the situation as I can. Note that it would be solely my own interpretation, and a case of explaining results that we see, rather than ...

4

As you noted, the chlorine and the other group being eliminated must be antiperiplanar. In the case of the chair form of cyclohexane, this means that the chlorine and other group being eliminated must be trans-diaxial. In the figure below I've drawn the 2 possible conformations (interconverted by a chair flip) for your deuterated cyclohexane. Only in the ...

Only top voted, non community-wiki answers of a minimum length are eligible