Is it correct to assign the following name: 4-ethyl-5-isopropyl-3-heptene? I fear not: the longest chain is the one with more substituents, if I'm not mistaken. Therefore, I would say: 4,5-diethyl-6-methyl-3-heptene.
Thanks for a confirmation.

https://www.handymath.com/cgi-bin/nitrictble2.cgi?submit=Entry
The Organic Syntheses prep indicates that the fuming nitric acid they used had a specific gravity of 1.51.  I have found various densities for both 90% and 98% nitric acid, and I am not sure which value is correct.*  Just now I found a table on line.  At 25° C, 70% has a density of 1.406; 90% has a density of 1.483, and 98% has a density of 1.501.  Therefore, I am not sure whether this protocol is for 90% or 98% nitric acid, but l lean toward the hypothesis that the author used 98%.
*A ThermoFisher web page gives the density of 90% nitric acid as 1.5110, which is questionable.  At a FisherSci web page there is 90% nitric acid from Thermo Scientific and the density is given as 1.41, which is very questionable.

By the way, there is also uncertainty regarding the names of the various concentrations of nitric acid.  One source indicated that red fuming nitric acid is 98% and white fuming nitric acid is 90%, but I do not think that everyone adheres to this convention.  For example Sigma Aldrich has a product "nitric acid, red fuming" that they list as >90%, but it is unclear what the exact percentage is.

Here is a nice chance to write a classic paper! Sort out all this question marks by making all these concentrations and measure density and observe color. A bit dangerous, but it could get a lot of reads and citations. It could end up with that It's not very important for nitration what concentration you use if you try their reactivity on a model molecule.

https://www.handymath.com/cgi-bin/nitrictble2.cgi?submit=Entry
The Organic Syntheses prep indicates that the fuming nitric acid they used had a specific gravity of 1.51.  I have found various densities for both 90% and 98% nitric acid, and I am not sure which value is correct.*  Just now I found a table on line.  At 25° C, 70% has a density of 1.406; 90% has a density of 1.483, and 98% has a density of 1.501.  Therefore, I am not sure whether this protocol is for 90% or 98% nitric acid, but l lean toward the hypothesis that the author used 98%.
*A ThermoFisher web page gives the density of 90% nitric acid as 1.5110, which is questionable.  At a FisherSci web page there is 90% nitric acid from Thermo Scientific and the density is given as 1.41, which is very questionable.

By the way, there is also uncertainty regarding the names of the various concentrations of nitric acid.  One source indicated that red fuming nitric acid is 98% and white fuming nitric acid is 90%, but I do not think that everyone adheres to this convention.  For example Sigma Aldrich has a product "nitric acid, red fuming" that they list as >90%, but it is unclear what the exact percentage is.

At your suggestion I found that reference yesterday.  My understanding is that acetyl nitrate is the species that is reacting with the substrate.

My mistake.  A colleague of mine suggested looking at old Organic Syntheses preparations.

At your suggestion I found that reference yesterday.  My understanding is that acetyl nitrate is the species that is reacting with the substrate.