WEBVTT 00:00:16.100 --> 00:00:24.966 Welcome everybody! Today we will present to you a feature of the iOrgChem website, specifically how to practice with the assignment of chirality 00:00:24.966 --> 00:00:32.099 more specifically, how to practice with the assignment of chirality of R or S configurations 00:00:32.100 --> 00:00:35.900 Let's start by opening the web page... 00:00:35.900 --> 00:00:44.733 ...and on the horizontal menu, at the item Exercises, choose the sub-item "Chirality? Hands on! A step-by-step guide" 00:00:46.900 --> 00:00:58.733 We can see two panels: in the left one we can draw a molecule in 2D and in the right one we wiil be able to see the 3D molecule 00:00:58.733 --> 00:01:10.633 just on the right we have the possibiltiy to select the background colour for the 3D panel: white or black to have a better contrast of the image 00:01:10.633 --> 00:01:20.899 at the right edge we have several buttons, useful to practice assigning the chirality with a "step-by-step" method. 00:01:20.900 --> 00:01:26.766 By scrolling down the page by the mouse... 00:01:26.766 --> 00:01:38.332 ...we can see some instructions to be followed, for a proficient use of the page, by assigning the R or S configuration and check the results. 00:01:38.333 --> 00:01:42.733 finally, some sections are reported below: 00:01:42.733 --> 00:01:50.566 1) Sequence Rules; 2) Correct Oreintation of the Molecule; 3) Configuration Assignment 00:01:50.566 --> 00:01:59.266 by clicking on them you can find information for the configruation assignment of a chiral carbon 00:02:03.066 --> 00:02:13.099 Let's start by drawing a simple molecule with a carbon substituted by four different groups... 00:02:13.100 --> 00:02:17.100 ...a propyl group.... 00:02:17.100 --> 00:02:21.100 ...a hydroxyl group... 00:02:21.100 --> 00:02:23.533 ...a methyl group... 00:02:23.533 --> 00:02:26.066 ...and a chlorine atom 00:02:26.066 --> 00:02:31.799 If we want to be precise, like when we are drawing molecules taken from a book... 00:02:31.800 --> 00:02:40.633 we "must" take care to draw the molecule in a correct way, in particular the stereochemical bonds, wedged and hash-wedged! 00:02:40.633 --> 00:02:51.666 In this case, we can draw the wedged bond connecting the chiral carbon to the hydroxy group and the hash-wedged one for the chlorine 00:02:51.666 --> 00:02:59.566 Once we have finshed drawing the molecule we can select the button "2D to 3D"... 00:02:59.566 --> 00:03:04.699 ...and the 3D structure will appear in the right panel in a few seconds. 00:03:07.100 --> 00:03:11.100 first of all, let's click on the "initialize" button to set up the process. 00:03:11.100 --> 00:03:16.700 ...and select the chiral carbon by the mouse. 00:03:16.700 --> 00:03:20.700 Please pay attention "NOT" to rotate/move the molecule, otherwise the atom will not be selected! 00:03:20.700 --> 00:03:26.900 By clicking with the mouse left button on the "C" button the "C" label will appear on the chiral center 00:03:26.900 --> 00:03:36.400 Once we have defined the chiral center, we can use the same method to attribute the priority to the four substituents... 00:03:36.400 --> 00:03:43.366 so, click on the chlorine and attribute to it the priority "1"... 00:03:43.366 --> 00:03:47.366 ...priority "2" to the hydroxyl group... 00:03:47.366 --> 00:03:50.766 ...priority "3" to the propyl group... 00:03:50.766 --> 00:03:54.766 ...and priority "4" to the methyl group... 00:03:54.766 --> 00:04:05.032 pay attention: the propyl has higher priority than the methyl group: its first carbon is connected to a carbon while methyl has only hydrogens. 00:04:05.033 --> 00:04:18.833 Now we have to move the molecule to orient it with lowest priority group (methyl) pointing away from the observer. 00:04:24.133 --> 00:04:27.533 Now we are ready to assign the chirality! 00:04:27.533 --> 00:04:39.299 to do it, let's have a look at the priority order. In order to go from 1 → 2 → 3, we need to follow a counterclockwise direction. Chirality is "S" 00:04:39.300 --> 00:04:44.766 in order to assign chirality, select the chiral carbon with the mouse... 00:04:44.766 --> 00:04:50.832 ...and click on the "S" button 00:04:50.833 --> 00:05:03.699 To check our answer about chirality, let's click with the mouse on the "Check Chirality" button. 00:05:03.700 --> 00:05:12.966 If the letter (R or S) we have drawn before on the chiral carbon does not change, we assigned the correct chirality.... 00:05:12.966 --> 00:05:15.299 ...otherwise, it will be incorrect. 00:05:15.300 --> 00:05:24.200 In this case, we are warmly suggested to check: 1) the priority we assigned before; 2) the orientation of the molecule. 00:05:24.200 --> 00:05:38.433 If we simply want to know the chirality, we can click on the "Show All Chiral Carbons" button. 00:05:38.433 --> 00:05:48.733 If there is more than one chiral carbon, we will be presented with the chirality assignment of all chiral carbons. 00:05:50.700 --> 00:06:01.900 We can advise you to see the two videos: "The chirality" and "The structural isomerism" (only in italian) 00:06:01.900 --> 00:06:06.900 Have a good study time!