When methyloxirane is treated with HBr, the bromide ion attacks the less substituted position. However, when phenyloxirane is tr
eated with HBr, the bromide ion attacks the more substituted position. Explain the difference in regiochemistry in terms of a competition between steric effects and electronic effects. (Hint: It may help to draw out the structure of the phenyl group.)
1 answer:
Answer:
See explanation and picture below
Explanation:
First, in the case of methyloxirane (Also known as propilene oxide) the mechanism that is taking place there is something similar to a Sn2 mechanism. Although a Sn2 mechanism is a bimolecular substitution taking place in only step, the mechanism followed here is pretty similar after the first step.
In both cases, the H atom of the HBr goes to the oxygen in the molecule. You'll have a OH⁺ in both. However, in the case of methyloxirane the next step is a Sn2 mechanism step, the bromide ion will go to the less substitued carbon, because the methyl group is exerting a steric hindrance. Not a big one but it has a little effect there, that's why the bromide will rather go to the carbon with more hydrogens. and the final product is formed.
In the case of phenyloxirane, once the OH⁺ is formed, the next step is a Sn1 mechanism. In this case, the bond C - OH⁺ is opened on the side of the phenyl to stabilize the OH. This is because that carbon is more stable than the carbon with no phenyl. (A 3° carbon is more stable than a 2° carbon). Therefore, when this bond opens, the bromide will go there in the next step, and the final product is formed. See picture below for mechanism and products.
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Answer:
If NO₂ molecule written is for Nitrogen dioxide, then, four of the five molecules presented above have no dipole moment and only one of the five molecules, Ozone (0₃), has a dipole moment.
But if the NO₂ molecule is for nitrite ion, NO₂⁻, then three out of the five molecules presented have no dipole moment and only the Nitrite ion, NO₂⁻, and Ozone, 0₃, have dipole moments.
Explanation:
- The Lewis Structure for the molecules are drawn in the image attached to this answer.
The bond dipole moment uses the idea of electric dipole moment to measure the polarity of a chemical bond within a molecule. It occurs whenever there is a separation of positive and negative charges. Polarity occurs due to differences in electronegativity.
1) Browne or Trihydridoboron, BH₃ - No dipole moment in the molecule.
Each B-H bond in BH₃ is polar/forms a dipole because the B and H atoms have different electronegativities. But, the shape of the molecule is trigonal planar which is symmetrical, so the dipoles/bond polarities cancel. The resulting BH₃ molecule is non-polar.
2)Nitrogen dioxide, NO₂ has no dipole moment.
Nitrite ion, NO₂⁻ -> Has a dipole moment.
There are two NO₂ molecules, the Nitrogen dioxide molecule is linear and has no dipole moment, but the NO₂⁻ ion is a polar molecule. The geometry of the molecule is bent because of a non-bonding pair of electrons. The bent geometry causes the polarity and subsequent dipole moment.
3) Sulfur hexafluoride, SF₆ - no dipole moment.
Sulfur hexafluoride, abbreviated as SF₆, is a nonpolar molecule. SF₆ has an octahedral molecular geometry, which means that the sulfur molecule has six fluorine atoms surrounding it. While each individual bond is polar, there is no net effect as symmetrical nature of this octahedral molecular structure means the dipole moments all cancel out, meaning that the molecule is nonpolar.
4) Ozone, O₃ - has a dipole moment.
O₃ is polar because there are 18 valence electrons, so the lewis structure would position the central O connected to one single bond and one double bond to connect the other O's. The lone pair on the central O would also mean the molecule was bent, thus making it polar. Therefore, Ozone is a polar molecule with a dipole moment of 0.53 D. The molecule can be represented as a resonance hybrid with two contributing structures, each with a single bond on one side and double bond on the other.
5) Phosphorus pentachloride, PCl₅
PCl₅ has a symmetrical geometry, the vector sum of the dipole moments of the different P-Cl bonds cancel each other. Therefore, the overall dipole moment of PCl₅ becomes 0.
Hope this helps!
