If I react a phosphorus ylide with trans-cinnamaldehyde, what would the ratio of trans-trans to cis-trans isomer would I likely get?
Cannnot get the exact ratio but the major product will be trans trans isomer since it's thermodynamically more favorable.
To determine the likely ratio of trans-trans to cis-trans isomer when reacting a phosphorus ylide with trans-cinnamaldehyde, you need to consider the mechanism of the reaction and the nature of the starting materials.
1. First, understand the reaction: The reaction you are referring to is a Wittig reaction, which involves the formation of a carbon-carbon double bond. A phosphorus ylide reacts with an aldehyde or ketone to produce an alkene.
2. Analyze the starting materials: In this case, you have trans-cinnamaldehyde, which is a trans-α,β-unsaturated aldehyde. The trans configuration indicates that the two substituents on the double bond are on opposite sides of the plane.
3. Consider the stereoselectivity: The stereoselectivity of the Wittig reaction depends on the nature of the phosphorus ylide. If the ylide is stabilized by bulky groups, it will preferentially react with the less crowded face of the aldehyde or ketone, resulting in predominantly trans product. If the ylide is not strongly stabilized, it may also undergo reaction on the crowded face, leading to some cis product.
4. Determine the likely ratio: In general, when using a standard phosphorus ylide, the trans-trans isomer is favored. This is because the bulkiness of the phosphorus ylide stabilizes the intermediate and promotes reaction of the less sterically hindered face of the aldehyde. Therefore, you would likely obtain a higher ratio of trans-trans isomer compared to the cis-trans isomer.
However, the ratio of trans-trans to cis-trans isomer may also depend on the specific phosphorus ylide used and the reaction conditions. Experimental verification or computational methods can provide more accurate predictions of the product ratios in specific cases.