What makes compound aromatic

In the trans , cis , trans, cis, cis isomer, the molecule is cyclic, conjugated, and has 10 pi electrons, but the two marked hydrogens bump into one another when attempting to adopt a flat conformation. The molecule is prevented from adopting planarity due to this punitive Van Der Waals strain , and is therefore not aromatic. Interestingly, if the hydrogens are removed and replaced with a bridging CH 2 group, the strain is relieved and the pi bonds can adopt a planar conformation. The molecule below right shows the expected properties of an aromatic molecule.

Check out these worked examples. Weird case: the one with aromaticity around the exterior but not on the inside. The wikipedia article covers it well. In pyrrole out of the distal and proximal carbons wrt N which are more electron densed? For pyrrole, C-3 is more nucleophilic.

Where is the empty p orbital in the phenyl carbocation in relation to the pi-system? Therein lies your answer. That is just not right then, is it? It can either be that it gets a singular electron in the newly occupied orbital or that its p-Orbital electron is drawn out to the new one. Thank you! If you were to have a triangle carbon structure with one lone pair and no double bond; would that still count as aromatic due to resonance?

I have a test tomorrow and am confused in this. Hi James, great post! Why is the molecule with the interior sp3 hybridized carbons listed as having 10 pi electrons rather than 14? So, is fulvene anti-aromatic or non-aromatic? Is it because the p-orbital on the ch2 outside of the ring does not have good overlap with any of the carbons inside the ring?

Non aromatic. If it were antiaromatic it would not be isolable. The p orbital on the ch2 outside of the ring is not part of the cyclic array of p orbitals. However this is not enough to make it truly aromatic. Hi, for cyclopentadienyl carbanion, a comment on rehybridization from sp3 typical in carbanion species to sp2 to get some benefits from resonance stabilization since it is adjacent to other sp2 hybridized carbons should be given.

Great job! Will there be any changes about aromaticity? The furan oxygen will be sp2. In the p orbital will be a lone pair of electrons, aligned with the other p-orbitals in the pi system. The other lone pair will be in the same plane of the molecule as the C-H bonds. If there is a system of 2 fused rings in which one is fully conjugated but other one has sp3 carbon , so will that structure be considered as aromatic since one ring is aromatic? Well, one ring is aromatic and the other is clearly not.

Think of it as a substituted benzene derivative. Think about the rules for aromaticity and work through it.

Is it cyclic? Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. A prototypical aromatic compound is benzene, so a layperson might prefer to think of an aromatic compound as something that has a ring structure like that of benzene, C 6 H 6.

Chill out with laboratory condensers from Safety Emporium. For those with limited chemistry experience, in the drawings of benzene above there are six pi-electrons.

If you look at the first or third drawing, the double lines bonds between carbon atoms each have 2 pi-electrons. There are 3 double bonds in these drawings, and therefore six pi-electrons. Aspiring chemists will note that our current discussion is omitting a feature of aromatic molecules called resonance that explains their chemical properties.

For detailed information about the special chemical properties and chemistry of aromatic molecules, see the Further Reading links below. The term "aromatic" was used by chemists to describe certain chemicals with peculiar odors long before anyone understood what atoms were or how they might be connected to form molecules.

Many aromatic molecules such as benzene and those shown below have distinctive odors aromas , but not all aromatic molecules have an odor. This stability is lost in electrophilic addition because the product is not aromatic.

Aromatic compounds are produced from a variety of sources, including petroleum and coal tar. Poly-aromatic hydrocarbons are components of atmospheric pollution and are known carcinogens. Aromatic compounds are also interesting because of their presumed role in the origin of life as precursors to nucleotides and amino acids. Boundless vets and curates high-quality, openly licensed content from around the Internet.

This particular resource used the following sources:. An aromatic must follow four basic criteria: it must be a ring planar, have a continuous chain of unhybridized p orbitals a series of sp 2 -hybridized atoms forming a conjugated system , and have an odd number of delocalized electron pairs in the system. Furan is planar ring fulfilling criteria and , and its oxygen atom has a choice of being sp 3 -hybridized or sp 2 -hybridized.

Depending on what hybridization the oxygen atom chooses will determine whether the molecule is aromatic or not. If the oxygen is sp 3 -hybridized, the molecule will not have a continuous chain of unhybridized p orbitals, and will not be considered aromatic it will be non-aromatic. If the oxygen is sp 2 -hybridized, it will fulfill criterion. Placing one of its lone pairs into the unhybridized p orbital will add two more electrons into the conjugated system, bringing the total number of electrons to or, it will have pairs of electrons.

Because it has an odd number of delocalized electrons it fulfills criterion , and therefore the molecule will be considered aromatic.

Because an aromatic molecule is more stable than a non-aromatic molecule, and by switching the hybridization of the oxygen atom the molecule can achieve aromaticity, a furan molecule will be considered an aromatic molecule. This molecule cannot be considered aromatic because this sp 3 carbon cannot switch its hybridization it has no lone pairs. Therefore, it fails to follow criterion and is not considered an aromatic molecule. It is a non-aromatic molecule.

If the molecule fails any of the first three criteria, it is considered non-aromatic, and if it fails the only the fourth criterion it has an even number of delocalized electron pairs , the molecule is considered antiaromatic. In the case of cyclobutadiene, by virtue of its structure follows criteria and. However, it violates criterion by having two an even number of delocalized electron pairs. Although it's possible that a molecule can try to escape from being antiaromatic by contorting its 3D shape so it is not planar, cyclobutadiene is too small to do this effectively.

Therefore, cyclobutadiene is considered antiaromatic. If you've found an issue with this question, please let us know. With the help of the community we can continue to improve our educational resources. If Varsity Tutors takes action in response to an Infringement Notice, it will make a good faith attempt to contact the party that made such content available by means of the most recent email address, if any, provided by such party to Varsity Tutors.

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Hanley Rd, Suite St. Louis, MO Subject optional. Email address: Your name:. Which compound s shown above is are aromatic? Possible Answers: A. Correct answer: A. Explanation : For a compound to be considered aromatic, it must be flat, cyclic, and conjugated and it must obey Huckel's rule. Report an Error. Example Question 2 : Identifying Aromatic Compounds. Which of the compounds below is antiaromatic, assuming they are all planar?

Possible Answers: 14 Annulene. Correct answer: 8 Annulene. Explanation : The correct answer is 8 Annulene. Example Question 3 : Identifying Aromatic Compounds.