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Latest Message: 2 days, 12 hours ago
- Dr. S. Gevorg : They are lower in energy compared to the syn conformation, but gauche is still higher than anti - check this post: https://www.chemistrysteps.com/newman-projections/. Go over these posts to see the difference between steric and torsional strain: https://www.chemistrysteps.com/steric-vs-torsional-strain/, then this one describing the energies of different conformations: https://www.chemistrysteps.com/gauche-conformation-steric-torsional-strain-energy-practice-problems/
- ralmachnee : How do i describe the sterics of a staggered gauche compared to a staggered anti when they are both low in energy?
- Dr. S. Gevorg : Frost circles have some too - https://www.chemistrysteps.com/frost-circle/, the endo product in Diels Alder reactions - https://www.chemistrysteps.com/endo-and-exo-products-of-diels-alder-reaction/. Depends in what context you need it, your textbook should give you the foundations.
- Dr. S. Gevorg : There is a section about it in the post on the SN2 mechanism - https://www.chemistrysteps.com/sn2-nucleophilic-substitution-reaction-mechanism/, but no dedicated discussion as such.
- guest_5112 : Where can I find stuff about the antibonding and bonding orbital?
- Dr. S. Gevorg : Regarding conjugation and hyperconjugation, they are related concepts because both involve electron delocalization that stabilizes a molecule. However, they are not the same. Conjugation refers to the overlap of adjacent π orbitals or p orbitals, while hyperconjugation involves the donation of electron density from a σ bond (usually C–H or C–C) into a neighboring empty or partially filled p orbital or π system. They both require parallel orbital alignment: https://www.chemistrysteps.com/localized-delocalized-lone-pairs/, https://www.chemistrysteps.com/resonance-and-conjugated-dienes/
- Dr. S. Gevorg : The reason for stabilization via hyperconjugation is the decrease ofthe overall energy level of the molecule. In general, bonding orbitals are lower energy/more stable compared to nonbonding/empty orbitals, so when the empty orbital is supplied with tlectron it "becomes" or resembles a bonding orbital and the system gets some stabilization.
- Dr. S. Gevorg : An empty p orbital can be present in different species, such as Lewis acids and carbocations, which, in turn, can form, for example, by loss of a leaving group or protonation of a C=C double bond. The key at this point is that you go over the hybridization theory, which will help you understand why a carbon with three bonds and no lone pairs has an empty p orbital, as well as how pi bonds are formed. Do not overlook the importance of hybridization and VSEPR theory, as they are the foundation of understanding organic structures.
- ralmachnee : Can you also explain why hyperconjugation is stabilizing?
- ralmachnee : And is hyper conjugation not related to pi conjugation?
- ralmachnee : So what is an empty p orbital? And Pi bonds are formed from unhybridized p orbitals correct?
- Dr. S. Gevorg : Newman projections are just one way of showing molecules, so they are not related to hypercojugation as such. You may have seen it represented with Newman projections because they are great for showing bond and orbital alignment, but that is all there is to correlating Newman projections with hyperconjugation. The interaction does not restrict the number of electron-donating orbitals, and yes, it occurs most often between C-H sigma bonds and empty p orbitals of carbocations.
- ralmachnee : Like I am confused on it because is it always in newman projections and is it always one filled orbital overalps with one empty orbital and does that orbital have to be a p orbital or does it not matter?
- Dr. S. Gevorg : Is there a specific question you are working on?
- Dr. S. Gevorg : @ralmachnee: A few posts, including https://www.chemistrysteps.com/stability-of-carbocations/, have it mentioned.
- ralmachnee : Do you have anything about hyperconjugation?
- Adithya : I have sent it
- Dr. S. Gevorg : No worries, it's on the contact page.
- Adithya : Thanks a Million Mr Gevorg. Would you give the the id
- Dr. S. Gevorg : Send me an email
- Adithya : Ok But how do I post an image here
- Dr. S. Gevorg : Feel free to post it here if you have a specific example of a molecule with more than one complex substituent, and we'll discuss it.
- Dr. S. Gevorg : 5-ethyl should go before all the dimethyls. I will need to think about such an example where two bis or tri determine the alphabetical priority. They don't normally do that - we ignore the prefixes.
- Adithya : If possible would you be kind enough to give me an example involving a tiebreaker for the complex Substituent part
- Adithya : So what is the name of the organic compound which I have given. Is the same which I have mentioned or is it different
- Dr. S. Gevorg : None of the prefixes such as di, tri, tetra, sec-, tert- are considered for alphabetical priority except the -iso.
- Dr. S. Gevorg : Adithya : Ok, so there is only one complex substituent in this molecule, and that is 1,1-dimethylethyl, which is tert-butyl. The ones you mentioned earlier – bis, tris, tetrakis, etc. – are used to tell the number of complex substituents, so you won’t need them here. As for the regular di-, tri-, etc., we do not consider them unless they are the only tiebreakers. For example, dimethyl beats trimethyl, and methyl itself will have a higher priority than a methyl with any prefix.
- Adithya : The doubt arose, when I was dealing with the below question : 5-(1,1-dimethylethyl)-5-ethyl-4,6-dimethyldecane . In this is the di in the methyl of Complex Substituent (in the brackets) considered and the di int the methyl of Simple Substituent coming just before the word root not considered
- Dr. S. Gevorg : @Adithya: I would say no, unless everything else is the same in the names, then we'd look at the alphabetical order of these prefixes.
- Adithya : In naming of Complex Substituent, Do we have to consider the alphabetical order of bis, tetrakis etc and the bi, tri, (which comes inside the complex Substituent part)
- Adithya : In naming of Complex Substituent, Do we have to consider
- Dr. S. Gevorg : @guest_758Shahana: I have replied to your question in the comments below - please check there.
- Dr. S. Gevorg : @Varu T: Constitutional isomers are compounds with the same molecular formula but different connectivity of atoms. Therefore, all isomers of C₃H₆O must satisfy this rule. So yes, for C₃H₆O, the different structures you can draw are constitutional (functional) isomers as long as the atoms are connected differently. Keto–enol tautomers are also constitutional isomers because of the connectivity changes, even though they can interconvert.
- guest_758Shahana : I face trouble to elucidate structure while reading of HSQC and HMBC . how to elucidate structure from HSQC and HMBC .plz can you guide me how i clear my confusion related the topic in NMR . I mostly face problem to search mechanism of different organic reactions . is there any website where i can check mechanism of any reaction?
- Varu T : Sir please reply.
- Varu T : Thankyou so much sir, sir I have one more doubt, for the molecular formula C3H6O, there are 6 functional isomers( propanal, propanone, methoxy ethene, oxirane, oxitane and prop-2-en-1-ol ). Am i right?? And sir prop-1-enol and prop-1-en-2-ol will not be considered functional isomers because they will show tautomerism . Is this correct? This is what my chemistry tution teacher told me. By the way sir I am from New Delhi. Have you ever been to India?
- Dr. S. Gevorg : @Varu T: All students are welcome. Yes, these two represent the same compound, although 1-Chloro-2-methylbenzene is likely the official IUPAC name.
- guest_6778 : ☹️ plz tell sir
- Varu T : 1 chloro 2 methyl benzene and 2 chlorotoluene are the iupac names of same compound?
- Varu T : Sir do you answer questions of indian students? I also have some doubts
- Dr. S. Gevorg : @guest_3289: Hi there, nice to hear from you! Feel free to ask any questions here.
- guest_3289 : im not a member though
- guest_3289 : and thanks for this amazing useful website
- guest_3289 : I just want to say hi
- Dr. S. Gevorg : @ MattTan: Yes, please check the board
- MattTan : Could someone tell me a quick way to approach the problem I posted for Ozonolysis?
- Dr. S. Gevorg : https://www.chemistrysteps.com/is-phenyl-an-ortho-para-or-meta-director/
- guest_6934 : g
- guest_6934 : is beneze+i or -i and ist it +m or -m
- guest_6934 : is ph a bulky group?
- Dr. S. Gevorg : https://www.chemistrysteps.com/acetal-hydrolysis-mechanism/
- guest_57 : hydrolysise of aceta
- Dr. S. Gevorg : @guest_4122 - Hello, I do have an entire section on General Chemistry at https://general.chemistrysteps.com/
- guest_4122 : Hi, do you have a guide that covers the course Chem 30A : basic chemical principles: nomenclature, atomic structure, quantum theory, molecular structure and bonding, periodic properties, chemical reactions, stoichiometry, thermochemistry, states of matter, gas laws, solutions, oxidation-reductions, and molecular equilibrium?
- Dr. S. Gevorg : @Anna: Sure, you can use the board to ask your question
- Anna : Need help with structure elucidation
- Dr. S. Gevorg : @Joujoulou: Hi there, you can read about the general trends of acidity in these posts: https://www.chemistrysteps.com/how-resonance-affects-acidity-and-basicity/, https://www.chemistrysteps.com/factors-determine-pka-acid-strength/
- Joujoulou : Good afternoon, do you have practice problems on the structure and properties of carboxylic acid and substituent effects on acidity?
- Dr. S. Gevorg : @Joujoulou: Hello, You can find most topics on carboxylic acids, including practice problems on specific functional groups, from the home page or the index page. For example, practice problems on the reactions of esters: https://www.chemistrysteps.com/ester-reactions-summary-and-practice-problems/ In addition, you can download the Study Guides on carboxylic acid derivatives at https://www.chemistrysteps.com/cs-benefits/ , as well as the reaction map of carboxylic acid derivatives at https://www.chemistrysteps.com/organic-chemistry-reaction-maps/. We also have multiple-choice quizzes, including one on carboxylic acid derivatives. It is quite a long chapter and, although you will need to memorize certain things, try to recognize the patterns. Most of the reactions are nucleophilic addition-elimination reactions, which you should be familiar with from the aldehydes and ketones chapter. Doing lots of practice problems is what ultimately makes it possible.
- Joujoulou : im currently learning about carboxylic acid and derivatives
- Joujoulou : Also, how would you memorize reagents? I was thinking of doing practice problems on each reagent individually and then doing it all together
- Joujoulou : Hi, are there any practice problems where I can only do practice problems on one thing, like esters, for example?
- Dr. S. Gevorg : @edentippets Although it is a topic of discussion on its own, there are really a handful of nucleophiles that you need to know. These are mainly oxygen-, nitrogen-, sulfur-containing species, and their negative counterparts, i.e. the conjugate bases are stronger nucleophiles. Carbanions are also excellent nucleophiles and strong bases. When it is a strong base and nucleophile, you always need to watch out for E2 reactions. Here, we have the most common nucleophiles listed according to their reactivity: https://www.chemistrysteps.com/nucleophiles-and-electrophiles/. Check also the post on comparing the SN2 and E2 reactions: https://www.chemistrysteps.com/sn2-vs-e2/
- edentippets : How do I know if a nucleophile is strong or weak?
- Dr. S. Gevorg : @guest_5893 That is an SN2 reaction, and more specifically, we can classify it as a Williamson ether synthesis. Check these two posts for more details: https://www.chemistrysteps.com/sn2-nucleophilic-substitution-reaction-mechanism/, https://www.chemistrysteps.com/williamson-ether-synthesis/
- guest_5893 : Need help with bimolecular transition state of guaifenesin synthesis. Drawing the curved arrow mechanism between 2-methoxyphenoxide and 3 chloro-1,2-propanediol
- khalum : I have a question on reaction arrows
- guest_5206 : structure for Start: Draw AMC with -NH2 at position 7 and -CH3 at position 4.Step 1: Show AMC with Boc on the amino group (replace -NH2 with -NH-Boc).Step 2: Draw Boc-Phe-OH (Boc-NH-CH(R)-COOH, R = phenyl).Step 3: Arrow showing coupling reaction with DCC/HOBt. Show formation of amide bond between AMC’s amino nitrogen (deprotected) and Phe’s carboxyl carbon.Step 4: Show removal of Boc from Phe’s amino group with TFA.Step 5: Add next amino acid with Boc protection and repeat coupling arrow.S
- Dr. S. Gevorg : @djtka - Hello, please tell me how I can help you. You can use the board to draw structures
- djtka : hi, I need help with e and z. im confused and would like to talk this through the way I do it
- Dr. S. Gevorg : @eyee0000 Check this post for finding the most acidic proton, and the related articles for other topics in acid-base chemistry: https://www.chemistrysteps.com/how-to-find-the-most-acidic-proton/
- eyee0000 : I need help finding the most acidic H atom on a molecule and reaction arrows of reactions based on pKa values and PES for reactions
- Dr. S. Gevorg : @guest_1908 Hi there
- guest_1908 : hello good evening
- Dr. S. Gevorg : @ guest_7827ab : Please ask a specific question so people can help you.
- guest_7827ab : help with stereoisomers
- guest_7827ab : Help with stereoisomers
- guest_9455 : Nomenclature of Thiols, Ethers, Alkyl Halides, and Others
- guest_9455 : Nomenclature of Thiols, Ethers, Alkyl Halides, and Others
- Dr. S. Gevorg : Hello, no, not about polymers
- bahareh.moalemia : Hi, Do we have a Topic of Monomers and Polymer in this chemistry program?
- Dr. S. Gevorg : Welcome to the Study Hall! Be the first to ask your question.
Once someone has answered your question, use the main board ☝️ to continue the discussion – it’s cleaner, faster, and without notification sounds. Simply click on the object on the board, add your comment, and continue the dialogue from there.
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which one is smallest aromatic compounds benzene or train gul shap with 1 singer bond and one positive charge on it?
You need to explain yourself better. What is train gul shap ?
Nomenclature of Thiols, Ethers, Alkyl Halides, and Others
Can you explain this
Yes, they can be found here, and if you have a specific question, you can ask here or under the comments of these posts.
Hi
I need help with stereoisomers, chiral centres, R and S con figuration
Go ahead, Raphaella
I’m having difficulties finding naming R and S configurations
There are two components there, yes? 1) You need to know the IUPAC rules to name the molecule. 2) You need to be able to determine the R and S configuration. First, name the molecule as if it does not have any chiral centers, then add the configurations of these chiral centers with the corresponding locants, i.e., 4R, 3S. Do you have a specific example? You can draw that on the board.
I face trouble to elucidate structure while reading of HSQC and HMBC . how to elucidate structure from HSQC and HMBC .plz can you guide me how i clear my confusion related the topic in NMR .
I mostly face problem to search mechanism of different organic reactions . is there any website where i can check mechanism of any reaction?
HSQC and HMBC are 2D NMR correlation techniques – HSQC shows direct ¹H–¹³C (one-bond) correlations, while HMBC shows long-range (2-3 bond) H–C correlations. If you already know how to interpret ¹H and ¹³C NMR, using HSQC and HMBC together is usually not very difficult, they mainly help you connect protons to the correct carbons. That said, without a specific spectrum or example, it’s hard to generalize how to solve every case.
As for reaction mechanisms, don’t we all wish there were a website that could draw the mechanism for any reaction 🙂 Unfortunately, chemistry doesn’t quite work that way. However, most common mechanisms and recurring patterns in undergraduate organic chemistry are covered here on Chemistry Steps, as well as on other organic chemistry websites and YouTube channels. Once you learn the patterns, you can usually reason out the mechanism yourself.
Thank you sir for answering. Sir I somehow able to interpret structure of organic compound by taking help from HNMR and C-NMR spectra and some how from Molecular formula .but in our course there is topics of COSY, HSQC ,HMBC .and I get sometimes failed to interpret and elucidate structure and in simple way the use of HSQC and HMBC . how I can read and elucidate any structure . can you plz sir guide me or having any notes etc or recommended video etc. Plz sir I will be much grateful.
Hello Shahana,
Glad to hear you’re making progress with ¹H and ¹³C NMR! As I mentioned before, HSQC and HMBC are just tools to connect protons to the right carbons and reveal longer-range correlations. If you keep practicing with specific examples and spectra, it will gradually become much easier to interpret.
Other than your professor’s notes, you may also want to check out textbooks on organic structure determination and look for additional online materials and videos. Sorry for not being too specific – this is a specialized topic, and I would recommend asking your professor for further guidance to really master it. With practice, reading 2D NMR becomes a natural extension of what you already know from 1D NMR.
Ok sir thank you so much for guidance.