Orient each of the following drawings so that the lowest-ranked group is toward the rear, and th

Orient each of the following drawings so that the...

Key Concepts

R/S Configuration Assignment

Once the molecule is properly oriented, the R (rectus) or S (sinister) configuration is determined by following the sequence of substituents from highest to lowest priority. If the sequence progresses in a clockwise direction, the configuration is R; if it progresses counterclockwise, the configuration is S. This method provides an unambiguous way to describe the three-dimensional arrangement of atoms around a chiral center.

Molecular Orientation for Stereochemical Analysis

Before assigning a configuration, it is essential to orient the molecule so that the substituent with the lowest priority (often the smallest or least reactive group) is positioned away from the observer. This standard view ensures that the observed sequence of substituents can be correctly interpreted in terms of their spatial arrangement.

Cahn-Ingold-Prelog Priority Rules

These rules provide a standardized method to assign priorities to the substituents attached to a stereocenter. Each substituent is ranked based on atomic number and further connectivity, which is fundamental to accurately determining the stereochemistry of a molecule.

Transcript

00:01 They want us to orient each of the following drawings, so the lowest -train group is towards the rear, and then they want us to assign r or an s configuration.

00:10 So let's go ahead and start with a here.

00:13 Well, notice for a, we already have four in the back, so we actually don't need to do anything.

00:18 That one's good.

00:20 Now, to determine if this is going to be r or s, now we need to rotate going in whatever direction, 1, 2, and 3 are, since 3 is in the back.

00:31 So it's going to be like this here.

00:37 And so notice that this is going to the left.

00:41 So the way i like to remember for r and s, i'll draw this off on the side here.

00:45 So when you draw an s, when you first start drawing it, you start up top here.

00:50 So this is going to the left.

00:54 And normally when you first start drawing in r, when you draw the hook part, notice how you go to the right.

01:04 Or you can just remember r is to the right and s is the other one.

01:10 So notice how we're going to the left here.

01:13 So this is going to be s.

01:15 Now what about this other one here? well, we have two in the back and four over here.

01:22 So what we can do is pinch one here and then rotate these other groups.

01:29 Because remember single pause we can rotate like this.

01:33 So we're going to keep one the same, but four gets rotated to two, two gets rotated to three, and then three gets rotated to like, oh, actually i don't know what i did there...

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