The special "hollow" arrows are called retrosynthetic arrows and they represent a reversed action when planning a synthesis. "Normal" arrows in a reaction indicate "makes" or "goes to" whereas "retrosynthetic" arrows are read as "comes from." So, using a normal arrow an alcohol "goes to" a ketone in an oxidation whereas using a retrosynthetic arrow a ketone "comes from" an alcohol via oxidation. Hope that helps!

بتزاكر الدرس قبل الامتحان بشهر يا يهودي

Hello! The mechanism for halogenation enforces anti addition of the two bromine atoms, however the product shown @ 2:50 is drawn using "ordinary" lines to depict covalent bonds. Because it does not use "dash-wedge" bonds nor Fischer projection the drawing does not convey any stereochemical information. Swapping the position of the bromine attached to the left carbon with either of the two methyl groups would actually represent the exact same structure, because the structure (using "ordinary" lines) does not depict any specific arrangement of atoms in 3D space. Also, keep in mind that the product can (and will) undergo free rotation, which allows the two bromine atoms to adopt positions that are "cis" or "trans" to each other. BTW, in this specific example, no new chiral centers are formed. Even if "dash-wedge" bonds had been used they would not add any additional information; when fewer than two new chiral centers are formed, we cannot tell whether a reaction was syn or anti stereoselective. Attributing spatial information to structures that use only "ordinary" lines to depict covalent bonds is a common mistake! Just because the bonds are pointing in the same direction (up in this case) doesn't mean they are actually cis to each other. As an exercise, draw a skeletal structure of 1,2-dibromocyclohexane using only "ordinary" lines. The structure will look like the two bromine atoms are "cis" to each other, but in reality the drawing could be representing either the cis or trans isomer. I hope this helps!

@@LOCStudios Thank you so much Dr. Aaron for your response!

Hello! The examples in the video are not from a book. I created the examples for use in my organic chemistry classes and then also used them here.

@@LOCStudios Great job! well done

Thanks! Let us know if you have other chemistry concepts you'd like us to explain!